diff --git a/docs/protocol.md b/docs/protocol.md
index 4d0fcce..00b8781 100644
--- a/docs/protocol.md
+++ b/docs/protocol.md
@@ -1,4 +1,4 @@
-# Wire protocol v4
+# Wire protocol v5
 
 The client talks to the server two ways:
 
@@ -65,6 +65,10 @@ Placeable (non-abstract) types plus labels in `lang`, and the last-wins `maps/de
 `core` plus the listed extras. The server always prepends `core`. `mods` is a comma-separated
 list of extra pack ids; omit it for vanilla. Unknown extras return `400` `unknown-mod`.
 
+Room slots include a `count` (how many of the default thing the def places). Things carry
+`pupilSlots` — how many pupils that thing hosts for lessons. The create editor copies both onto
+the map instance; the snapshot's per-node pupil-slot total is computed on the server.
+
 `lang` is the same value Hello carries — not `Accept-Language`. Anything other than `en` is
 Russian.
 
@@ -243,9 +247,12 @@ Each node:
 | string | instance id |
 | string | parent id (empty for the yard) |
 | string | display name |
-| `u8` | item count, then that many strings |
+| `u16` | pupil slots — how many pupils can take a lesson here. Summed from things on the server. |
+| `u8` | item count, then that many records of: string name + `u8` count |
 | `u8` | position count, then that many strings |
 
+Item `count` is how many of that thing stand in the room (`Парта ×16` is one record, not sixteen). The client must not recompute pupil slots from items.
+
 ## Guarantees and limits
 
 - **Inbound** frames larger than 8 KiB are refused with close status `1009 MessageTooBig`. That
@@ -258,7 +265,7 @@ Each node:
   the oldest, because a stale clock is worthless once a newer one exists.
 - The map snapshot uses a separate reliable queue so ticks cannot crowd it out.
 
-## Not in v4 yet
+## Not in v5 yet
 
 Authentication, Sit orders, an event log, and `OpenLocation` on the server — the tree is filtered
 on the client from the snapshot. The school's ECS world is created but still empty.
diff --git a/src/HSchool.Client/src/i18n/strings.test.ts b/src/HSchool.Client/src/i18n/strings.test.ts
index 117e602..fcd17d8 100644
--- a/src/HSchool.Client/src/i18n/strings.test.ts
+++ b/src/HSchool.Client/src/i18n/strings.test.ts
@@ -20,6 +20,7 @@ describe('t', () => {
   it('interpolates placeholders', () => {
     setLocale('en');
     expect(t('schoolCount', { current: 2, max: 6 })).toBe('Schools: 2 of 6.');
+    expect(t('pupilSlots', { count: 16 })).toBe('Pupil places: 16');
   });
 });
 
diff --git a/src/HSchool.Client/src/i18n/strings.ts b/src/HSchool.Client/src/i18n/strings.ts
index 1a1fb62..b0408ac 100644
--- a/src/HSchool.Client/src/i18n/strings.ts
+++ b/src/HSchool.Client/src/i18n/strings.ts
@@ -62,6 +62,7 @@ const ru = {
   addRoom: 'Добавить комнату',
   removeRoom: 'Удалить комнату',
   slotEmpty: '— пусто —',
+  slotCount: 'Количество',
 
   backToMenu: '← В главное меню',
   pause: 'Пауза',
@@ -76,6 +77,7 @@ const ru = {
   locationActivities: 'Сейчас',
   locationPositions: 'Должности',
   itemsEmpty: 'Пусто.',
+  pupilSlots: 'Ученических мест: {count}',
   charactersEmpty: 'Никого нет.',
   activitiesEmpty: 'Ничего не происходит.',
   positionsEmpty: 'Нет должностей.',
@@ -145,6 +147,7 @@ const en: Messages = {
   addRoom: 'Add room',
   removeRoom: 'Remove room',
   slotEmpty: '— empty —',
+  slotCount: 'Count',
 
   backToMenu: '← Main menu',
   pause: 'Pause',
@@ -159,6 +162,7 @@ const en: Messages = {
   locationActivities: 'Now',
   locationPositions: 'Positions',
   itemsEmpty: 'Empty.',
+  pupilSlots: 'Pupil places: {count}',
   charactersEmpty: 'Nobody here.',
   activitiesEmpty: 'Nothing is happening.',
   positionsEmpty: 'No positions.',
diff --git a/src/HSchool.Client/src/net/api.ts b/src/HSchool.Client/src/net/api.ts
index fd193ec..cb482de 100644
--- a/src/HSchool.Client/src/net/api.ts
+++ b/src/HSchool.Client/src/net/api.ts
@@ -71,11 +71,13 @@ export interface ModInfo {
 export interface DefInfo {
   readonly defName: string;
   readonly label: string;
+  readonly pupilSlots?: number;
 }
 
 export interface RoomSlotInfo {
   readonly key: string;
   readonly thing: string;
+  readonly count: number;
 }
 
 export interface RoomInfo {
@@ -95,7 +97,7 @@ export interface MapLayout {
     building: string;
     floor: string;
     label?: string;
-    slots?: { key: string; thing: string }[];
+    slots?: { key: string; thing: string; count?: number }[];
   }[];
   links: { a: string; b: string }[];
 }
diff --git a/src/HSchool.Client/src/net/protocol.test.ts b/src/HSchool.Client/src/net/protocol.test.ts
index 573957d..940414d 100644
--- a/src/HSchool.Client/src/net/protocol.test.ts
+++ b/src/HSchool.Client/src/net/protocol.test.ts
@@ -129,7 +129,7 @@ describe('decodeServerMessage', () => {
     const id = encoder.encode('yard');
     const parent = encoder.encode('');
     const name = encoder.encode('Двор');
-    const buffer = new ArrayBuffer(7 + 1 + 2 + id.length + 2 + parent.length + 2 + name.length + 1 + 1);
+    const buffer = new ArrayBuffer(7 + 1 + 2 + id.length + 2 + parent.length + 2 + name.length + 2 + 1 + 1);
     const view = new DataView(buffer);
     view.setUint8(0, MessageType.ServerMapSnapshot);
     view.setInt32(1, 7, true);
@@ -147,6 +147,8 @@ describe('decodeServerMessage', () => {
     offset += 2;
     new Uint8Array(buffer).set(name, offset);
     offset += name.length;
+    view.setUint16(offset, 0, true);
+    offset += 2;
     view.setUint8(offset, 0);
     offset += 1;
     view.setUint8(offset, 0);
@@ -155,7 +157,64 @@ describe('decodeServerMessage', () => {
       type: 'map-snapshot',
       schoolId: 7,
       nodes: [
-        { kind: 0, id: 'yard', parentId: '', name: 'Двор', items: [], positions: [] },
+        { kind: 0, id: 'yard', parentId: '', name: 'Двор', pupilSlots: 0, items: [], positions: [] },
+      ],
+    });
+  });
+
+  it('reads stacked items and pupil slots at the documented offsets', () => {
+    const encoder = new TextEncoder();
+    const id = encoder.encode('classroom-1a');
+    const parent = encoder.encode('floor-1');
+    const name = encoder.encode('Класс 1A');
+    const itemName = encoder.encode('Парта');
+    const buffer = new ArrayBuffer(
+      7 + 1 + 2 + id.length + 2 + parent.length + 2 + name.length + 2 + 1 + 2 + itemName.length + 1 + 1,
+    );
+    const view = new DataView(buffer);
+    view.setUint8(0, MessageType.ServerMapSnapshot);
+    view.setInt32(1, 1, true);
+    view.setUint16(5, 1, true);
+    let offset = 7;
+    view.setUint8(offset, 3);
+    offset += 1;
+    view.setUint16(offset, id.length, true);
+    offset += 2;
+    new Uint8Array(buffer).set(id, offset);
+    offset += id.length;
+    view.setUint16(offset, parent.length, true);
+    offset += 2;
+    new Uint8Array(buffer).set(parent, offset);
+    offset += parent.length;
+    view.setUint16(offset, name.length, true);
+    offset += 2;
+    new Uint8Array(buffer).set(name, offset);
+    offset += name.length;
+    view.setUint16(offset, 16, true);
+    offset += 2;
+    view.setUint8(offset, 1);
+    offset += 1;
+    view.setUint16(offset, itemName.length, true);
+    offset += 2;
+    new Uint8Array(buffer).set(itemName, offset);
+    offset += itemName.length;
+    view.setUint8(offset, 16);
+    offset += 1;
+    view.setUint8(offset, 0);
+
+    expect(decodeServerMessage(buffer)).toEqual({
+      type: 'map-snapshot',
+      schoolId: 1,
+      nodes: [
+        {
+          kind: 3,
+          id: 'classroom-1a',
+          parentId: 'floor-1',
+          name: 'Класс 1A',
+          pupilSlots: 16,
+          items: [{ name: 'Парта', count: 16 }],
+          positions: [],
+        },
       ],
     });
   });
diff --git a/src/HSchool.Client/src/net/protocol.ts b/src/HSchool.Client/src/net/protocol.ts
index 6aa312d..cb01956 100644
--- a/src/HSchool.Client/src/net/protocol.ts
+++ b/src/HSchool.Client/src/net/protocol.ts
@@ -5,7 +5,7 @@
  * changed together and documented in `docs/protocol.md`. All numbers are little-endian.
  */
 
-export const PROTOCOL_VERSION = 4;
+export const PROTOCOL_VERSION = 5;
 
 export const MessageType = {
   ClientHello: 0x01,
@@ -69,12 +69,18 @@ export const MapNodeKind = {
   Room: 3,
 } as const;
 
+export interface MapSnapshotItem {
+  readonly name: string;
+  readonly count: number;
+}
+
 export interface MapSnapshotNode {
   readonly kind: number;
   readonly id: string;
   readonly parentId: string;
   readonly name: string;
-  readonly items: readonly string[];
+  readonly pupilSlots: number;
+  readonly items: readonly MapSnapshotItem[];
   readonly positions: readonly string[];
 }
 
@@ -236,13 +242,18 @@ function decodeMapSnapshot(view: DataView): MapSnapshotMessage {
     offset = parentId.next;
     const name = readString(view, offset);
     offset = name.next;
+    ensure(view, offset + 2);
+    const pupilSlots = view.getUint16(offset, true);
+    offset += 2;
     const itemCount = readU8(view, offset);
     offset += 1;
-    const items: string[] = [];
+    const items: MapSnapshotItem[] = [];
     for (let item = 0; item < itemCount; item++) {
       const value = readString(view, offset);
-      items.push(value.text);
       offset = value.next;
+      const count = readU8(view, offset);
+      offset += 1;
+      items.push({ name: value.text, count });
     }
 
     const positionCount = readU8(view, offset);
@@ -254,7 +265,15 @@ function decodeMapSnapshot(view: DataView): MapSnapshotMessage {
       offset = value.next;
     }
 
-    nodes.push({ kind, id: id.text, parentId: parentId.text, name: name.text, items, positions });
+    nodes.push({
+      kind,
+      id: id.text,
+      parentId: parentId.text,
+      name: name.text,
+      pupilSlots,
+      items,
+      positions,
+    });
   }
 
   return { type: 'map-snapshot', schoolId, nodes };
diff --git a/src/HSchool.Client/src/style.css b/src/HSchool.Client/src/style.css
index cec7cae..df43785 100644
--- a/src/HSchool.Client/src/style.css
+++ b/src/HSchool.Client/src/style.css
@@ -317,6 +317,12 @@ body {
   font-size: 13px;
 }
 
+.panel__meta {
+  margin: 6px 0 0;
+  color: var(--text-muted);
+  font-size: 13px;
+}
+
 .tree {
   margin: 0;
   padding: 0;
@@ -542,6 +548,11 @@ body {
   flex: 1;
 }
 
+.field__row > .input--count {
+  flex: 0 0 4.5rem;
+  width: 4.5rem;
+}
+
 .field .hint {
   margin: 0;
   font-size: 13px;
diff --git a/src/HSchool.Client/src/ui/gameScreen.ts b/src/HSchool.Client/src/ui/gameScreen.ts
index 6fa5140..c1c90a0 100644
--- a/src/HSchool.Client/src/ui/gameScreen.ts
+++ b/src/HSchool.Client/src/ui/gameScreen.ts
@@ -1,4 +1,4 @@
-import { CLOCK_SPEEDS, type ClockMessage, type MapSnapshotNode } from '../net/protocol.ts';
+import { CLOCK_SPEEDS, type ClockMessage, type MapSnapshotItem, type MapSnapshotNode } from '../net/protocol.ts';
 import { formatGameDate, formatGameTimeOfDay, formatGameWeekday } from '../format/gameTime.ts';
 import { t } from '../i18n/strings.ts';
 import type { School } from '../net/api.ts';
@@ -36,6 +36,7 @@ export class GameScreen {
   private readonly itemsHeading = el('h3', { class: 'panel__section-title' });
   private readonly itemsEmpty = el('p', { class: 'panel__empty' });
   private readonly itemsList = el('ul', { class: 'panel__list' });
+  private readonly pupilSlotsLine = el('p', { class: 'panel__meta' });
   private readonly charactersHeading = el('h3', { class: 'panel__section-title' });
   private readonly charactersEmpty = el('p', { class: 'panel__empty' });
   private readonly activitiesHeading = el('h3', { class: 'panel__section-title' });
@@ -101,7 +102,7 @@ export class GameScreen {
             'div',
             { class: 'panel__body' },
             this.locationName,
-            el('div', { class: 'panel__section' }, this.itemsHeading, this.itemsEmpty, this.itemsList),
+            el('div', { class: 'panel__section' }, this.itemsHeading, this.itemsEmpty, this.itemsList, this.pupilSlotsLine),
             el('div', { class: 'panel__section' }, this.charactersHeading, this.charactersEmpty),
             el('div', { class: 'panel__section' }, this.activitiesHeading, this.activitiesEmpty),
             el('div', { class: 'panel__section' }, this.positionsHeading, this.positionsEmpty, this.positionsList),
@@ -210,7 +211,10 @@ export class GameScreen {
 
     const node = this.nodes.find((candidate) => candidate.id === this.selectedId);
     this.locationName.textContent = node?.name ?? '';
-    paintList(this.itemsList, this.itemsEmpty, node?.items ?? []);
+    paintList(this.itemsList, this.itemsEmpty, (node?.items ?? []).map(formatItem));
+    const pupilSlots = node?.pupilSlots ?? 0;
+    this.pupilSlotsLine.hidden = pupilSlots <= 0;
+    this.pupilSlotsLine.textContent = pupilSlots > 0 ? t('pupilSlots', { count: pupilSlots }) : '';
     paintList(this.positionsList, this.positionsEmpty, node?.positions ?? []);
   }
 
@@ -236,6 +240,10 @@ function childrenOf(nodes: readonly MapSnapshotNode[], parentId: string): MapSna
   return nodes.filter((node) => node.parentId === parentId);
 }
 
+function formatItem(item: MapSnapshotItem): string {
+  return item.count === 1 ? item.name : `${item.name} ×${item.count}`;
+}
+
 function paintList(list: HTMLUListElement, empty: HTMLParagraphElement, values: readonly string[]): void {
   clear(list);
   empty.hidden = values.length > 0;
diff --git a/src/HSchool.Client/src/ui/mapEditor.ts b/src/HSchool.Client/src/ui/mapEditor.ts
index 18b7c61..e5104d1 100644
--- a/src/HSchool.Client/src/ui/mapEditor.ts
+++ b/src/HSchool.Client/src/ui/mapEditor.ts
@@ -116,15 +116,29 @@ export function mapEditor(options: MapEditorOptions): {
 
       const fill = (room.slots ?? []).find((candidate) => candidate.key === slot.key);
       select.value = fill?.thing ?? '';
-      select.addEventListener('change', () => {
+
+      const countInput = el('input', { class: 'input input--count', type: 'number' });
+      countInput.min = '1';
+      countInput.max = '255';
+      countInput.step = '1';
+      countInput.value = String(fill?.count ?? slot.count ?? 1);
+      countInput.title = t('slotCount');
+
+      const writeSlot = (): void => {
         const slots = [...(room.slots ?? [])].filter((candidate) => candidate.key !== slot.key);
         if (select.value !== '') {
-          slots.push({ key: slot.key, thing: select.value });
+          const parsed = Number.parseInt(countInput.value, 10);
+          const count = Number.isFinite(parsed) ? Math.min(255, Math.max(1, parsed)) : (slot.count ?? 1);
+          countInput.value = String(count);
+          slots.push({ key: slot.key, thing: select.value, count });
         }
 
         room.slots = slots;
         emit();
-      });
+      };
+
+      select.addEventListener('change', writeSlot);
+      countInput.addEventListener('change', writeSlot);
 
       rows.push(
         el(
@@ -132,6 +146,7 @@ export function mapEditor(options: MapEditorOptions): {
           { class: 'field__row' },
           el('span', { class: 'field__label', text: slot.key }),
           select,
+          countInput,
         ),
       );
     }
@@ -288,8 +303,8 @@ function hasLink(map: MapLayout, a: string, b: string): boolean {
   );
 }
 
-function defaultSlots(def: RoomInfo): { key: string; thing: string }[] {
-  return def.slots.map((slot) => ({ key: slot.key, thing: slot.thing }));
+function defaultSlots(def: RoomInfo): { key: string; thing: string; count: number }[] {
+  return def.slots.map((slot) => ({ key: slot.key, thing: slot.thing, count: slot.count }));
 }
 
 function nextId(prefix: string, used: Set<string>): string {
diff --git a/src/HSchool.Content/CatalogLoader.cs b/src/HSchool.Content/CatalogLoader.cs
index b4bd9af..721a23c 100644
--- a/src/HSchool.Content/CatalogLoader.cs
+++ b/src/HSchool.Content/CatalogLoader.cs
@@ -352,6 +352,11 @@ public sealed class CatalogLoader
     {
         foreach (var thing in catalog.Things.Values)
         {
+            if (thing.PupilSlots < 0 || thing.PupilSlots > byte.MaxValue)
+            {
+                throw new ContentLoadException($"ThingDef '{thing.DefName}' pupilSlots must be 0–{byte.MaxValue}.");
+            }
+
             foreach (var action in thing.Actions)
             {
                 if (!catalog.Actions.ContainsKey(action))
@@ -369,6 +374,11 @@ public sealed class CatalogLoader
                 {
                     throw new ContentLoadException($"RoomDef '{room.DefName}' slot '{slot.Key}' references unknown ThingDef '{slot.Thing}'.");
                 }
+
+                if (slot.Count < 0 || slot.Count > byte.MaxValue)
+                {
+                    throw new ContentLoadException($"RoomDef '{room.DefName}' slot '{slot.Key}' count must be 0–{byte.MaxValue}.");
+                }
             }
 
             foreach (var position in room.Positions)
diff --git a/src/HSchool.Content/Defs.cs b/src/HSchool.Content/Defs.cs
index b00286d..24864cc 100644
--- a/src/HSchool.Content/Defs.cs
+++ b/src/HSchool.Content/Defs.cs
@@ -27,6 +27,12 @@ public sealed class ActionDef : Def;
 public sealed class ThingDef : Def
 {
     public IReadOnlyList<string> Actions { get; init; } = [];
+
+    /// <summary>
+    /// How many pupils this thing hosts for lessons. Zero for teacher's furniture — a chair
+    /// must not inflate class size just because someone sits in it.
+    /// </summary>
+    public int PupilSlots { get; init; }
 }
 
 public sealed class PositionDef : Def;
diff --git a/src/HSchool.Content/MapLayout.cs b/src/HSchool.Content/MapLayout.cs
index dd18dee..ec0ef11 100644
--- a/src/HSchool.Content/MapLayout.cs
+++ b/src/HSchool.Content/MapLayout.cs
@@ -63,6 +63,12 @@ public sealed class SlotFill
     public required string Key { get; init; }
 
     public required string Thing { get; init; }
+
+    /// <summary>
+    /// How many of <see cref="Thing"/> occupy this slot. Missing or non-positive JSON is 1, so
+    /// older maps without a count still round-trip.
+    /// </summary>
+    public int Count { get; init; } = 1;
 }
 
 public sealed class MapLink
diff --git a/src/HSchool.Content/MapValidator.cs b/src/HSchool.Content/MapValidator.cs
index b916970..fe8ef2d 100644
--- a/src/HSchool.Content/MapValidator.cs
+++ b/src/HSchool.Content/MapValidator.cs
@@ -140,6 +140,11 @@ public static class MapValidator
             {
                 throw new MapValidationException($"Room '{room.Id}' slot '{fill.Key}' uses unknown or abstract ThingDef '{fill.Thing}'.");
             }
+
+            if (fill.Count > byte.MaxValue)
+            {
+                throw new MapValidationException($"Room '{room.Id}' slot '{fill.Key}' count {fill.Count} is above {byte.MaxValue}.");
+            }
         }
     }
 
diff --git a/src/HSchool.Content/MapView.cs b/src/HSchool.Content/MapView.cs
index d7fefc6..b861f90 100644
--- a/src/HSchool.Content/MapView.cs
+++ b/src/HSchool.Content/MapView.cs
@@ -21,11 +21,17 @@ public sealed class MapViewNode
 
     public required string Name { get; init; }
 
-    public IReadOnlyList<string> Items { get; init; } = [];
+    public IReadOnlyList<MapViewItem> Items { get; init; } = [];
+
+    /// <summary>Sum of <c>ThingDef.PupilSlots × fill count</c> for this node. Zero off rooms.</summary>
+    public int PupilSlots { get; init; }
 
     public IReadOnlyList<string> Positions { get; init; } = [];
 }
 
+/// <summary>One stacked thing in a room. The client formats <c>Парта ×16</c>; this is the data.</summary>
+public sealed record MapViewItem(string Name, int Count);
+
 /// <summary>
 /// Builds the location tree the client draws. Labels come from the frozen catalog in the
 /// requested locale; people and in-place activities are not part of this view.
@@ -47,6 +53,7 @@ public static class MapView
                 parentId: string.Empty,
                 LabelOf(catalog, locale, DefKind.Territory, territory.Def),
                 items: [],
+                pupilSlots: 0,
                 PositionsOf(catalog, locale, DefKind.Territory, territory.Def)),
         };
 
@@ -58,6 +65,7 @@ public static class MapView
                 territory.Id,
                 LabelOf(catalog, locale, DefKind.Building, building.Def),
                 [],
+                pupilSlots: 0,
                 PositionsOf(catalog, locale, DefKind.Building, building.Def)));
         }
 
@@ -69,23 +77,20 @@ public static class MapView
                 floor.Building,
                 FloorName(catalog, locale, floor),
                 [],
+                pupilSlots: 0,
                 PositionsOf(catalog, locale, DefKind.Floor, floor.Def)));
         }
 
         foreach (var room in map.Rooms)
         {
-            var items = new List<string>(room.Slots.Count);
-            foreach (var fill in room.Slots)
-            {
-                items.Add(LabelOf(catalog, locale, DefKind.Thing, fill.Thing));
-            }
-
+            var (items, pupilSlots) = RoomContents(catalog, locale, room);
             nodes.Add(Node(
                 MapNodeKind.Room,
                 room.Id,
                 room.Floor,
                 RoomName(catalog, locale, room),
                 items,
+                pupilSlots,
                 PositionsOf(catalog, locale, DefKind.Room, room.Def)));
         }
 
@@ -97,7 +102,8 @@ public static class MapView
         string id,
         string parentId,
         string name,
-        IReadOnlyList<string> items,
+        IReadOnlyList<MapViewItem> items,
+        int pupilSlots,
         IReadOnlyList<string> positions) =>
         new()
         {
@@ -106,9 +112,33 @@ public static class MapView
             ParentId = parentId,
             Name = name,
             Items = items,
+            PupilSlots = pupilSlots,
             Positions = positions,
         };
 
+    private static (IReadOnlyList<MapViewItem> Items, int PupilSlots) RoomContents(
+        DefCatalog catalog,
+        string locale,
+        RoomNode room)
+    {
+        var items = new List<MapViewItem>(room.Slots.Count);
+        var pupilSlots = 0L;
+        foreach (var fill in room.Slots)
+        {
+            var count = SlotQuantity(fill.Count);
+            items.Add(new MapViewItem(LabelOf(catalog, locale, DefKind.Thing, fill.Thing), count));
+            if (catalog.Things.TryGetValue(fill.Thing, out var thing) && thing.PupilSlots > 0)
+            {
+                pupilSlots += (long)thing.PupilSlots * count;
+            }
+        }
+
+        return (items, (int)Math.Clamp(pupilSlots, 0, ushort.MaxValue));
+    }
+
+    private static int SlotQuantity(int count) =>
+        count < 1 ? 1 : Math.Min(count, byte.MaxValue);
+
     /// <summary>
     /// A floor's <see cref="FloorNode.Label"/> is its designation, not a replacement name — the
     /// vanilla map says "1". On its own that is a stray digit in the client's tree, so it follows
diff --git a/src/HSchool.Protocol/Messages.cs b/src/HSchool.Protocol/Messages.cs
index cb852b2..d6e1b3e 100644
--- a/src/HSchool.Protocol/Messages.cs
+++ b/src/HSchool.Protocol/Messages.cs
@@ -44,15 +44,21 @@ public readonly record struct ServerSchoolGoneMessage(int SchoolId);
 /// <summary>
 /// Tree node in a map snapshot. Kind is <c>0</c> territory, <c>1</c> building, <c>2</c> floor, <c>3</c> room.
 /// <paramref name="ParentId"/> is empty for the yard.
+/// <paramref name="PupilSlots"/> is how many pupils can take a lesson here — summed from things
+/// on the server, not by the client.
 /// </summary>
 public sealed record MapSnapshotNode(
     byte Kind,
     string Id,
     string ParentId,
     string Name,
-    IReadOnlyList<string> Items,
+    ushort PupilSlots,
+    IReadOnlyList<MapSnapshotItem> Items,
     IReadOnlyList<string> Positions);
 
+/// <summary>One stacked thing in a room. <paramref name="Count"/> is 1–255.</summary>
+public sealed record MapSnapshotItem(string Name, byte Count);
+
 /// <summary>
 /// One school's map, labelled in the Hello locale. Sent once when that school is opened, not every tick.
 /// People and in-place activities are omitted — the client keeps those sections empty.
diff --git a/src/HSchool.Protocol/ProtocolCodec.cs b/src/HSchool.Protocol/ProtocolCodec.cs
index a9b3971..2200130 100644
--- a/src/HSchool.Protocol/ProtocolCodec.cs
+++ b/src/HSchool.Protocol/ProtocolCodec.cs
@@ -116,11 +116,12 @@ public static class ProtocolCodec
         {
             size += sizeof(byte);
             size += StringSize(node.Id) + StringSize(node.ParentId) + StringSize(node.Name);
+            size += sizeof(ushort);
 
             size += sizeof(byte);
             foreach (var item in node.Items)
             {
-                size += StringSize(item);
+                size += StringSize(item.Name) + sizeof(byte);
             }
 
             size += sizeof(byte);
@@ -156,10 +157,12 @@ public static class ProtocolCodec
             writer.WriteString(node.Id);
             writer.WriteString(node.ParentId);
             writer.WriteString(node.Name);
+            writer.WriteUInt16(node.PupilSlots);
             writer.WriteByte((byte)node.Items.Count);
             foreach (var item in node.Items)
             {
-                writer.WriteString(item);
+                writer.WriteString(item.Name);
+                writer.WriteByte(item.Count);
             }
 
             writer.WriteByte((byte)node.Positions.Count);
@@ -263,11 +266,14 @@ public static class ProtocolCodec
             var id = reader.ReadString();
             var parentId = reader.ReadString();
             var name = reader.ReadString();
+            var pupilSlots = reader.ReadUInt16();
             var itemCount = reader.ReadByte();
-            var items = new string[itemCount];
+            var items = new MapSnapshotItem[itemCount];
             for (var item = 0; item < itemCount; item++)
             {
-                items[item] = reader.ReadString();
+                var itemName = reader.ReadString();
+                var count = reader.ReadByte();
+                items[item] = new MapSnapshotItem(itemName, count);
             }
 
             var positionCount = reader.ReadByte();
@@ -277,7 +283,7 @@ public static class ProtocolCodec
                 positions[position] = reader.ReadString();
             }
 
-            nodes[i] = new MapSnapshotNode(kind, id, parentId, name, items, positions);
+            nodes[i] = new MapSnapshotNode(kind, id, parentId, name, pupilSlots, items, positions);
         }
 
         return new ServerMapSnapshotMessage(schoolId, nodes);
diff --git a/src/HSchool.Protocol/ProtocolConstants.cs b/src/HSchool.Protocol/ProtocolConstants.cs
index 1455f02..dcd7dae 100644
--- a/src/HSchool.Protocol/ProtocolConstants.cs
+++ b/src/HSchool.Protocol/ProtocolConstants.cs
@@ -4,7 +4,7 @@ namespace HSchool.Protocol;
 public static class ProtocolConstants
 {
     /// <summary>Bumped on every breaking change to the binary layout.</summary>
-    public const byte Version = 4;
+    public const byte Version = 5;
 
     /// <summary>Upper bound for a single WebSocket frame accepted by the server.</summary>
     public const int MaxMessageSize = 8 * 1024;
diff --git a/src/HSchool.Server/Api/ModEndpoints.cs b/src/HSchool.Server/Api/ModEndpoints.cs
index 848b38a..7ecffa5 100644
--- a/src/HSchool.Server/Api/ModEndpoints.cs
+++ b/src/HSchool.Server/Api/ModEndpoints.cs
@@ -94,7 +94,7 @@ internal sealed record CatalogResponse(
             Placeable(catalog.Buildings.Values, catalog, locale),
             Placeable(catalog.Floors.Values, catalog, locale),
             PlaceableRooms(catalog, locale),
-            Placeable(catalog.Things.Values, catalog, locale),
+            PlaceableThings(catalog, locale),
             map);
 
     private static IReadOnlyList<DefInfoResponse> Placeable<T>(IEnumerable<T> defs, DefCatalog catalog, string locale)
@@ -105,6 +105,13 @@ internal sealed record CatalogResponse(
             .Select(def => new DefInfoResponse(def.DefName, catalog.Label(locale, def)))
             .ToArray();
 
+    private static IReadOnlyList<DefInfoResponse> PlaceableThings(DefCatalog catalog, string locale) =>
+        catalog.Things.Values
+            .Where(def => !def.Abstract)
+            .OrderBy(def => def.DefName, StringComparer.Ordinal)
+            .Select(def => new DefInfoResponse(def.DefName, catalog.Label(locale, def), def.PupilSlots))
+            .ToArray();
+
     private static IReadOnlyList<RoomInfoResponse> PlaceableRooms(DefCatalog catalog, string locale) =>
         catalog.Rooms.Values
             .Where(def => !def.Abstract)
@@ -112,12 +119,12 @@ internal sealed record CatalogResponse(
             .Select(def => new RoomInfoResponse(
                 def.DefName,
                 catalog.Label(locale, def),
-                def.Slots.Select(slot => new RoomSlotInfo(slot.Key, slot.Thing)).ToArray(),
+                def.Slots.Select(slot => new RoomSlotInfo(slot.Key, slot.Thing, slot.Count)).ToArray(),
                 def.Positions.ToArray()))
             .ToArray();
 }
 
-internal sealed record DefInfoResponse(string DefName, string Label);
+internal sealed record DefInfoResponse(string DefName, string Label, int PupilSlots = 0);
 
 internal sealed record RoomInfoResponse(
     string DefName,
@@ -125,4 +132,4 @@ internal sealed record RoomInfoResponse(
     IReadOnlyList<RoomSlotInfo> Slots,
     IReadOnlyList<string> Positions);
 
-internal sealed record RoomSlotInfo(string Key, string Thing);
+internal sealed record RoomSlotInfo(string Key, string Thing, int Count);
diff --git a/src/HSchool.Server/Game/SchoolWorker.cs b/src/HSchool.Server/Game/SchoolWorker.cs
index 6664573..b6851b5 100644
--- a/src/HSchool.Server/Game/SchoolWorker.cs
+++ b/src/HSchool.Server/Game/SchoolWorker.cs
@@ -449,12 +449,19 @@ internal sealed class SchoolWorker
         for (var i = 0; i < view.Count; i++)
         {
             var node = view[i];
+            var items = new MapSnapshotItem[node.Items.Count];
+            for (var item = 0; item < node.Items.Count; item++)
+            {
+                items[item] = new MapSnapshotItem(node.Items[item].Name, (byte)node.Items[item].Count);
+            }
+
             nodes[i] = new MapSnapshotNode(
                 (byte)node.Kind,
                 node.Id,
                 node.ParentId,
                 node.Name,
-                node.Items,
+                (ushort)node.PupilSlots,
+                items,
                 node.Positions);
         }
 
diff --git a/src/HSchool.Server/mods/core/defs/rooms/academic.jsonc b/src/HSchool.Server/mods/core/defs/rooms/academic.jsonc
index 25cc2f8..3ea58de 100644
--- a/src/HSchool.Server/mods/core/defs/rooms/academic.jsonc
+++ b/src/HSchool.Server/mods/core/defs/rooms/academic.jsonc
@@ -4,6 +4,7 @@
     "slots": [
       { "key": "board", "thing": "Blackboard" },
       { "key": "teacherDesk", "thing": "Desk" },
+      { "key": "teacherChair", "thing": "Chair" },
       { "key": "studentDesks", "thing": "StudentDesk", "count": 16 },
     ],
     "positions": ["Teacher"],
@@ -22,6 +23,7 @@
     "defName": "ComputerLab",
     "slots": [
       { "key": "teacherDesk", "thing": "Desk" },
+      { "key": "teacherChair", "thing": "Chair" },
       { "key": "computers", "thing": "Computer", "count": 12 },
     ],
     "positions": ["Teacher"],
diff --git a/src/HSchool.Server/mods/core/defs/things/furniture.jsonc b/src/HSchool.Server/mods/core/defs/things/furniture.jsonc
index 5876694..1f9825b 100644
--- a/src/HSchool.Server/mods/core/defs/things/furniture.jsonc
+++ b/src/HSchool.Server/mods/core/defs/things/furniture.jsonc
@@ -1,10 +1,10 @@
 [
   { "defName": "Blackboard" },
-  { "defName": "StudentDesk", "parent": "Desk", "actions": ["Sit"] },
+  { "defName": "StudentDesk", "parent": "Desk", "actions": ["Sit"], "pupilSlots": 1 },
   { "defName": "Bookshelf" },
   { "defName": "DiningTable" },
   { "defName": "Bench", "actions": ["Sit"] },
-  { "defName": "Computer" },
+  { "defName": "Computer", "pupilSlots": 1 },
   { "defName": "MedicalCouch" },
   { "defName": "Locker" },
 ]
diff --git a/src/HSchool.Server/mods/core/maps/default.jsonc b/src/HSchool.Server/mods/core/maps/default.jsonc
index 15e18ff..44252fa 100644
--- a/src/HSchool.Server/mods/core/maps/default.jsonc
+++ b/src/HSchool.Server/mods/core/maps/default.jsonc
@@ -23,7 +23,7 @@
       "slots": [
         { "key": "directorChair", "thing": "DirectorsChair" },
         { "key": "desk", "thing": "Desk" },
-        { "key": "guestChair", "thing": "Chair" },
+        { "key": "guestChair", "thing": "Chair", "count": 2 },
       ],
     },
     {
@@ -43,7 +43,7 @@
       "floor": "floor-1",
       "slots": [
         { "key": "table", "thing": "DiningTable" },
-        { "key": "chairs", "thing": "Chair" },
+        { "key": "chairs", "thing": "Chair", "count": 6 },
       ],
     },
     {
@@ -55,7 +55,8 @@
       "slots": [
         { "key": "board", "thing": "Blackboard" },
         { "key": "teacherDesk", "thing": "Desk" },
-        { "key": "studentDesks", "thing": "StudentDesk" },
+        { "key": "teacherChair", "thing": "Chair" },
+        { "key": "studentDesks", "thing": "StudentDesk", "count": 16 },
       ],
     },
     {
@@ -67,7 +68,8 @@
       "slots": [
         { "key": "board", "thing": "Blackboard" },
         { "key": "teacherDesk", "thing": "Desk" },
-        { "key": "studentDesks", "thing": "StudentDesk" },
+        { "key": "teacherChair", "thing": "Chair" },
+        { "key": "studentDesks", "thing": "StudentDesk", "count": 16 },
       ],
     },
     {
@@ -77,7 +79,7 @@
       "floor": "floor-1",
       "slots": [
         { "key": "counter", "thing": "DiningTable" },
-        { "key": "seats", "thing": "Chair" },
+        { "key": "seats", "thing": "Chair", "count": 8 },
       ],
     },
     { "id": "restroom-1", "def": "Restroom", "building": "main", "floor": "floor-1", "label": "1" },
@@ -102,7 +104,8 @@
       "slots": [
         { "key": "board", "thing": "Blackboard" },
         { "key": "teacherDesk", "thing": "Desk" },
-        { "key": "studentDesks", "thing": "StudentDesk" },
+        { "key": "teacherChair", "thing": "Chair" },
+        { "key": "studentDesks", "thing": "StudentDesk", "count": 16 },
       ],
     },
     {
@@ -114,7 +117,8 @@
       "slots": [
         { "key": "board", "thing": "Blackboard" },
         { "key": "teacherDesk", "thing": "Desk" },
-        { "key": "studentDesks", "thing": "StudentDesk" },
+        { "key": "teacherChair", "thing": "Chair" },
+        { "key": "studentDesks", "thing": "StudentDesk", "count": 16 },
       ],
     },
     {
@@ -124,7 +128,7 @@
       "floor": "floor-2",
       "slots": [
         { "key": "desk", "thing": "Desk" },
-        { "key": "shelves", "thing": "Bookshelf" },
+        { "key": "shelves", "thing": "Bookshelf", "count": 4 },
       ],
     },
     {
@@ -134,7 +138,8 @@
       "floor": "floor-2",
       "slots": [
         { "key": "teacherDesk", "thing": "Desk" },
-        { "key": "computers", "thing": "Computer" },
+        { "key": "teacherChair", "thing": "Chair" },
+        { "key": "computers", "thing": "Computer", "count": 12 },
       ],
     },
     { "id": "restroom-2", "def": "Restroom", "building": "main", "floor": "floor-2", "label": "2" },
@@ -144,7 +149,7 @@
       "building": "gym",
       "floor": "gym-floor",
       "slots": [
-        { "key": "benches", "thing": "Bench" },
+        { "key": "benches", "thing": "Bench", "count": 4 },
       ],
     },
     {
@@ -153,7 +158,7 @@
       "building": "gym",
       "floor": "gym-floor",
       "slots": [
-        { "key": "lockers", "thing": "Locker" },
+        { "key": "lockers", "thing": "Locker", "count": 12 },
       ],
     },
   ],
diff --git a/tests/HSchool.AppHost.Tests/GameSocketTests.cs b/tests/HSchool.AppHost.Tests/GameSocketTests.cs
index 2f723a1..f47f643 100644
--- a/tests/HSchool.AppHost.Tests/GameSocketTests.cs
+++ b/tests/HSchool.AppHost.Tests/GameSocketTests.cs
@@ -106,6 +106,10 @@ public class GameSocketTests(AppHostFixture fixture)
         Assert.Equal("floor-1", office.ParentId);
         Assert.Contains("Директор", office.Positions);
         Assert.NotEmpty(office.Items);
+        var classroom = Assert.Single(snapshot.Nodes, node => node.Id == "classroom-1a");
+        Assert.Equal(16, classroom.PupilSlots);
+        Assert.Contains(classroom.Items, item => item.Name == "Парта" && item.Count == 16);
+        Assert.Contains(classroom.Items, item => item.Name == "Стул" && item.Count == 1);
     }
 
     [Fact]
diff --git a/tests/HSchool.Content.Tests/MapViewTests.cs b/tests/HSchool.Content.Tests/MapViewTests.cs
index e0aef1f..a46e08f 100644
--- a/tests/HSchool.Content.Tests/MapViewTests.cs
+++ b/tests/HSchool.Content.Tests/MapViewTests.cs
@@ -23,12 +23,17 @@ public class MapViewTests
 
         var officeRu = ru.Single(node => node.Id == "principals-office");
         Assert.Equal("Кабинет директора", officeRu.Name);
-        Assert.Equal(["Кресло директора", "Стол", "Стул"], officeRu.Items);
+        Assert.Equal(
+            [new MapViewItem("Кресло директора", 1), new MapViewItem("Стол", 1), new MapViewItem("Стул", 2)],
+            officeRu.Items);
+        Assert.Equal(0, officeRu.PupilSlots);
         Assert.Equal(["Директор"], officeRu.Positions);
 
         var officeEn = en.Single(node => node.Id == "principals-office");
         Assert.Equal("Principal's office", officeEn.Name);
-        Assert.Equal(["Principal's chair", "Desk", "Chair"], officeEn.Items);
+        Assert.Equal(
+            [new MapViewItem("Principal's chair", 1), new MapViewItem("Desk", 1), new MapViewItem("Chair", 2)],
+            officeEn.Items);
         Assert.Equal(["Principal"], officeEn.Positions);
 
         var corridor = ru.Single(node => node.Id == "corridor-1");
@@ -38,7 +43,15 @@ public class MapViewTests
 
         var classroom = ru.Single(node => node.Id == "classroom-1a");
         Assert.Equal("Класс 1A", classroom.Name);
-        Assert.Equal(["Доска", "Стол", "Парта"], classroom.Items);
+        Assert.Equal(
+            [
+                new MapViewItem("Доска", 1),
+                new MapViewItem("Стол", 1),
+                new MapViewItem("Стул", 1),
+                new MapViewItem("Парта", 16),
+            ],
+            classroom.Items);
+        Assert.Equal(16, classroom.PupilSlots);
         Assert.Equal(["Учитель"], classroom.Positions);
         Assert.Equal("Classroom 1A", en.Single(node => node.Id == "classroom-1a").Name);
     }
diff --git a/tests/HSchool.Content.Tests/VanillaCoreTests.cs b/tests/HSchool.Content.Tests/VanillaCoreTests.cs
index 1a2ed05..2e4bec9 100644
--- a/tests/HSchool.Content.Tests/VanillaCoreTests.cs
+++ b/tests/HSchool.Content.Tests/VanillaCoreTests.cs
@@ -25,8 +25,20 @@ public class VanillaCoreTests
         Assert.True(catalog.Rooms.ContainsKey("Classroom"));
         Assert.Equal("Класс", catalog.Label("ru", catalog.Rooms["Classroom"]));
         Assert.Equal(["Teacher"], catalog.PositionsFor(DefKind.Room, "Classroom"));
+        Assert.Equal(1, catalog.Things["StudentDesk"].PupilSlots);
+        Assert.Equal(1, catalog.Things["Computer"].PupilSlots);
+        Assert.Equal(0, catalog.Things["Desk"].PupilSlots);
+        Assert.Equal(0, catalog.Things["Chair"].PupilSlots);
+        Assert.Contains(catalog.Rooms["Classroom"].Slots, slot => slot.Key == "teacherChair" && slot.Thing == "Chair");
+        Assert.Equal(16, catalog.Rooms["Classroom"].Slots.Single(slot => slot.Key == "studentDesks").Count);
         Assert.Equal(2, map.Buildings.Count);
         Assert.True(map.Rooms.Count >= 18, "Vanilla layout should look like a small school, not a stub.");
         Assert.Contains(map.Rooms, room => room.Id == "classroom-1a" && room.Label == "1A");
+        Assert.Equal(
+            16,
+            map.Rooms.Single(room => room.Id == "classroom-1a").Slots.Single(slot => slot.Key == "studentDesks").Count);
+        Assert.Contains(
+            map.Rooms.Single(room => room.Id == "classroom-1a").Slots,
+            slot => slot.Key == "teacherChair" && slot.Thing == "Chair");
     }
 }
diff --git a/tests/HSchool.Protocol.Tests/ProtocolCodecTests.cs b/tests/HSchool.Protocol.Tests/ProtocolCodecTests.cs
index f435b1f..0f41ca9 100644
--- a/tests/HSchool.Protocol.Tests/ProtocolCodecTests.cs
+++ b/tests/HSchool.Protocol.Tests/ProtocolCodecTests.cs
@@ -137,8 +137,15 @@ public class ProtocolCodecTests
     public void MapSnapshot_RoundTripsAndWritesHeaderOffsets()
     {
         var message = new ServerMapSnapshotMessage(7, [
-            new MapSnapshotNode(0, "yard", "", "Двор", [], []),
-            new MapSnapshotNode(3, "office", "floor-1", "Кабинет директора", ["Стул"], ["Директор"]),
+            new MapSnapshotNode(0, "yard", "", "Двор", 0, [], []),
+            new MapSnapshotNode(
+                3,
+                "office",
+                "floor-1",
+                "Кабинет директора",
+                0,
+                [new MapSnapshotItem("Стул", 2)],
+                ["Директор"]),
         ]);
         var buffer = new byte[ProtocolConstants.MaxMessageSize];
 
@@ -154,17 +161,47 @@ public class ProtocolCodecTests
         Assert.Equal("yard", read.Nodes[0].Id);
         Assert.Equal("", read.Nodes[0].ParentId);
         Assert.Equal("Двор", read.Nodes[0].Name);
-        Assert.Equal(["Стул"], read.Nodes[1].Items);
+        Assert.Equal(0, read.Nodes[0].PupilSlots);
+        Assert.Equal([new MapSnapshotItem("Стул", 2)], read.Nodes[1].Items);
         Assert.Equal(["Директор"], read.Nodes[1].Positions);
     }
 
+    [Fact]
+    public void MapSnapshot_WritesPupilSlotsAndStackedItemCount()
+    {
+        var message = new ServerMapSnapshotMessage(1, [
+            new MapSnapshotNode(
+                3,
+                "classroom-1a",
+                "floor-1",
+                "Класс 1A",
+                16,
+                [new MapSnapshotItem("Парта", 16)],
+                []),
+        ]);
+        var buffer = new byte[ProtocolCodec.MapSnapshotSize(message)];
+
+        var length = ProtocolCodec.WriteMapSnapshot(buffer, message);
+        var read = ProtocolCodec.ReadMapSnapshot(buffer.AsSpan(0, length));
+
+        Assert.Equal(16, read.Nodes[0].PupilSlots);
+        Assert.Equal([new MapSnapshotItem("Парта", 16)], read.Nodes[0].Items);
+    }
+
     [Fact]
     public void MapSnapshotSize_IsExactlyWhatTheWriterProduces()
     {
         var message = new ServerMapSnapshotMessage(7, [
-            new MapSnapshotNode(0, "yard", "", "Двор", [], []),
-            new MapSnapshotNode(2, "floor-1", "main", "Этаж 1", [], []),
-            new MapSnapshotNode(3, "office", "floor-1", "Кабинет директора", ["Стол", "Стул"], ["Директор"]),
+            new MapSnapshotNode(0, "yard", "", "Двор", 0, [], []),
+            new MapSnapshotNode(2, "floor-1", "main", "Этаж 1", 0, [], []),
+            new MapSnapshotNode(
+                3,
+                "office",
+                "floor-1",
+                "Кабинет директора",
+                0,
+                [new MapSnapshotItem("Стол", 1), new MapSnapshotItem("Стул", 2)],
+                ["Директор"]),
         ]);
 
         var size = ProtocolCodec.MapSnapshotSize(message);
@@ -179,7 +216,7 @@ public class ProtocolCodecTests
         // A player who keeps clicking "Add room" in the create editor gets past 8 KiB somewhere
         // around sixty furnished rooms. Sizing the buffer from the message is what keeps that
         // school openable instead of killing its worker thread on the first snapshot.
-        var nodes = new List<MapSnapshotNode> { new(0, "yard", "", "Двор", [], []) };
+        var nodes = new List<MapSnapshotNode> { new(0, "yard", "", "Двор", 0, [], []) };
         for (var i = 1; i <= 200; i++)
         {
             nodes.Add(new MapSnapshotNode(
@@ -187,7 +224,8 @@ public class ProtocolCodecTests
                 $"principals-office-{i}",
                 "floor-1",
                 "Кабинет директора",
-                ["Кресло директора", "Стол", "Стул"],
+                0,
+                [new MapSnapshotItem("Кресло директора", 1), new MapSnapshotItem("Стол", 1), new MapSnapshotItem("Стул", 2)],
                 ["Директор"]));
         }
 
@@ -201,7 +239,9 @@ public class ProtocolCodecTests
 
         Assert.Equal(nodes.Count, read.Nodes.Count);
         Assert.Equal("principals-office-200", read.Nodes[^1].Id);
-        Assert.Equal(["Кресло директора", "Стол", "Стул"], read.Nodes[^1].Items);
+        Assert.Equal(
+            [new MapSnapshotItem("Кресло директора", 1), new MapSnapshotItem("Стол", 1), new MapSnapshotItem("Стул", 2)],
+            read.Nodes[^1].Items);
     }
 
     [Fact]