diff --git a/DorkNet.Server.Tests/SubRoomMaxPlayersTests.cs b/DorkNet.Server.Tests/SubRoomMaxPlayersTests.cs
new file mode 100644
index 0000000..e801474
--- /dev/null
+++ b/DorkNet.Server.Tests/SubRoomMaxPlayersTests.cs
@@ -0,0 +1,164 @@
+using System.Net.Http.Headers;
+using System.Net.Http.Json;
+using System.Text.Json;
+using DorkNet.Server.Data;
+using DorkNet.Server.Data.Entities;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DorkNet.Server.Tests;
+
+/// <summary>
+/// Max players is a PER SUB-ROOM setting, adjustable from two places:
+///
+///   in-game  PUT rooms/{id}/subrooms/{sub}/maxplayers   (owner only — the
+///            "Max Player Count in This Subroom" slider)
+///   admin    PUT api/admin/v1/rooms/{id}/subrooms/{sub}/maxplayers
+///
+/// Both write the same <see cref="RoomSceneEntity.MaxPlayers"/>, so a change
+/// made in one place has to be visible from the other. That is the property
+/// worth pinning: two independent write paths onto one column drift silently,
+/// and the symptom (a slider that snaps back) looks like a client bug.
+///
+/// Kept distinct from the room's own <see cref="RoomEntity.MaxCapacity"/>,
+/// which is what the ROOM advertises and what matchmaking hands to
+/// RoomInstance.MaxCapacity. Reading the room-level figure off sub-room 0
+/// would collapse the two settings into one.
+/// </summary>
+public sealed class SubRoomMaxPlayersTests : IClassFixture<DorkNetServerFactory>
+{
+    private readonly DorkNetServerFactory _factory;
+
+    public SubRoomMaxPlayersTests(DorkNetServerFactory factory) => _factory = factory;
+
+    [Fact]
+    public async Task Owner_and_admin_edit_the_same_per_subroom_value()
+    {
+        using var setup = Client("rooms");
+        var owner = await GameClientSessionFactory.CreateAsync(setup, _factory.ApexDomain);
+        var admin = await GameClientSessionFactory.CreateAsync(setup, _factory.ApexDomain);
+
+        var roomId = 9_700_000 + Random.Shared.Next(1, 99_999);
+        await using (var scope = _factory.Services.CreateAsyncScope())
+        {
+            var db = scope.ServiceProvider.GetRequiredService<DorkNetDbContext>();
+            (await db.Players.FirstAsync(p => p.Id == admin.PlayerId)).IsAdmin = true;
+
+            db.Rooms.Add(new RoomEntity
+            {
+                Id = roomId,
+                Name = $"Caps{Guid.NewGuid():N}"[..18],
+                CreatorPlayerId = owner.PlayerId,
+                MaxCapacity = 12,
+            });
+            db.RoomScenes.Add(new RoomSceneEntity
+            { RoomId = roomId, Name = "Home", OrderIndex = 0, MaxPlayers = 8 });
+            db.RoomScenes.Add(new RoomSceneEntity
+            { RoomId = roomId, Name = "Arena", OrderIndex = 1, MaxPlayers = 8 });
+            await db.SaveChangesAsync();
+        }
+
+        // ── in-game: the owner's slider on sub-room 1 only ──────────────────
+        // Sent exactly as the client sends it. NLDBPDCNNCF.MNBPCGJNLNP(Int64,
+        // Int64, Int32) builds a BLNOGFGHIIF whose single JSON key is
+        // "maxPlayers" and issues it with verb 3 = PUT — NOT the form encoding
+        // most of its siblings use. Testing with a form would pass while the
+        // real client's body went unread.
+        using var ownerClient = Client("rooms", owner);
+        using var slider = await ownerClient.PutAsJsonAsync(
+            $"/rooms/{roomId}/subrooms/1/maxplayers", new { maxPlayers = 24 });
+        var sliderBody = await slider.Content.ReadAsStringAsync();
+        Assert.True(slider.IsSuccessStatusCode,
+            $"owner PUT maxplayers -> {(int)slider.StatusCode}: {sliderBody}");
+
+        // The client deserialises the reply as FGCPNAACHIK — the room-details
+        // shape — so the slider's own response has to carry the new value.
+        var echoed = JsonDocument.Parse(sliderBody).RootElement
+            .GetProperty("SubRooms").EnumerateArray()
+            .First(e => e.GetProperty("SubRoomId").GetInt64() == 1);
+        Assert.Equal(24, echoed.GetProperty("MaxPlayers").GetInt32());
+
+        // ── admin: reads what the owner just set, then edits sub-room 0 ─────
+        using var adminClient = Client("admin", admin);
+        var listed = await GetJsonAsync(adminClient, $"/api/admin/v1/rooms/{roomId}/subrooms");
+        var subRooms = listed.EnumerateArray()
+            .ToDictionary(e => e.GetProperty("subRoomId").GetInt32(),
+                          e => e.GetProperty("maxPlayers").GetInt32());
+
+        Assert.Equal(24, subRooms[1]);
+        Assert.Equal(8, subRooms[0]);
+
+        using var adminSet = await adminClient.PutAsJsonAsync(
+            $"/api/admin/v1/rooms/{roomId}/subrooms/0/maxplayers", new { MaxPlayers = 40 });
+        Assert.True(adminSet.IsSuccessStatusCode,
+            $"admin PUT maxplayers -> {(int)adminSet.StatusCode}: {await adminSet.Content.ReadAsStringAsync()}");
+
+        // ── the room's own details carry each sub-room's own figure ─────────
+        var details = await GetJsonAsync(ownerClient, $"/rooms/{roomId}");
+        var wire = details.GetProperty("SubRooms").EnumerateArray()
+            .ToDictionary(e => e.GetProperty("SubRoomId").GetInt64(),
+                          e => e.GetProperty("MaxPlayers").GetInt32());
+
+        Assert.Equal(40, wire[0]);
+        Assert.Equal(24, wire[1]);
+
+        // The room-level figure is the room's advertised capacity, NOT a copy
+        // of sub-room 0 — otherwise the admin edit above would have moved it.
+        Assert.Equal(12, details.GetProperty("MaxPlayers").GetInt32());
+    }
+
+    [Fact]
+    public async Task Admin_cap_is_clamped_to_a_joinable_range()
+    {
+        using var setup = Client("rooms");
+        var owner = await GameClientSessionFactory.CreateAsync(setup, _factory.ApexDomain);
+        var admin = await GameClientSessionFactory.CreateAsync(setup, _factory.ApexDomain);
+
+        var roomId = 9_800_000 + Random.Shared.Next(1, 99_999);
+        await using (var scope = _factory.Services.CreateAsyncScope())
+        {
+            var db = scope.ServiceProvider.GetRequiredService<DorkNetDbContext>();
+            (await db.Players.FirstAsync(p => p.Id == admin.PlayerId)).IsAdmin = true;
+            db.Rooms.Add(new RoomEntity
+            {
+                Id = roomId,
+                Name = $"Clamp{Guid.NewGuid():N}"[..18],
+                CreatorPlayerId = owner.PlayerId,
+            });
+            db.RoomScenes.Add(new RoomSceneEntity
+            { RoomId = roomId, Name = "Home", OrderIndex = 0, MaxPlayers = 8 });
+            await db.SaveChangesAsync();
+        }
+
+        using var adminClient = Client("admin", admin);
+
+        // 0 would make the sub-room unjoinable.
+        using var tooLow = await adminClient.PutAsJsonAsync(
+            $"/api/admin/v1/rooms/{roomId}/subrooms/0/maxplayers", new { MaxPlayers = 0 });
+        var low = JsonDocument.Parse(await tooLow.Content.ReadAsStringAsync()).RootElement;
+        Assert.Equal(1, low.GetProperty("maxPlayers").GetInt32());
+
+        using var tooHigh = await adminClient.PutAsJsonAsync(
+            $"/api/admin/v1/rooms/{roomId}/subrooms/0/maxplayers", new { MaxPlayers = 9999 });
+        var high = JsonDocument.Parse(await tooHigh.Content.ReadAsStringAsync()).RootElement;
+        Assert.Equal(80, high.GetProperty("maxPlayers").GetInt32());
+    }
+
+    private static async Task<JsonElement> GetJsonAsync(HttpClient client, string path)
+    {
+        using var response = await client.GetAsync(path);
+        var body = await response.Content.ReadAsStringAsync();
+        Assert.True(response.IsSuccessStatusCode, $"GET {path} -> {(int)response.StatusCode}: {body}");
+        return JsonDocument.Parse(body).RootElement.Clone();
+    }
+
+    private HttpClient Client(string host, GameClientSession? session = null)
+    {
+        var client = _factory.CreateClient(new() { AllowAutoRedirect = false });
+        client.BaseAddress = new Uri($"http://{host}.{_factory.ApexDomain}");
+        if (session is not null)
+            client.DefaultRequestHeaders.Authorization =
+                new AuthenticationHeaderValue("Bearer", session.AccessToken);
+        return client;
+    }
+}
diff --git a/DorkNet.Server/Controllers/API/Rooms/V2/RoomsController.cs b/DorkNet.Server/Controllers/API/Rooms/V2/RoomsController.cs
index 1ddac0c..222e6b4 100644
--- a/DorkNet.Server/Controllers/API/Rooms/V2/RoomsController.cs
+++ b/DorkNet.Server/Controllers/API/Rooms/V2/RoomsController.cs
@@ -2143,9 +2143,12 @@ public class RoomsController(
             // name-keyed reader, presence does.
             DataBlob = dataBlobName,
             DataBlobHash = (string?)null,
-            // Room-level cap mirrors sub-room 0, which is where the client
-            // reads it from for a single-sub-room room.
-            MaxPlayers = sceneRows is { Count: > 0 } ? sceneRows[0].MaxPlayers : 8,
+            // The room-level cap is the room's own advertised capacity, which is
+            // what RoomEntity.MaxCapacity exists for and what matchmaking hands
+            // to RoomInstance.MaxCapacity. Each sub-room carries its own
+            // MaxPlayers in the SubRooms array — they are separate settings, so
+            // this must not be read off sub-room 0.
+            MaxPlayers = room.MaxCapacity,
             // ToxMod is Rec Room's hosted voice moderation. There is no such
             // service here, so it is off — the client only uses this to decide
             // whether to show the indicator.
diff --git a/DorkNet.Server/Controllers/Admin/AdminController.cs b/DorkNet.Server/Controllers/Admin/AdminController.cs
index 59502d2..40a8195 100644
--- a/DorkNet.Server/Controllers/Admin/AdminController.cs
+++ b/DorkNet.Server/Controllers/Admin/AdminController.cs
@@ -1097,6 +1097,81 @@ public class AdminController(
         });
     }
 
+    /// <summary>GET <c>api/admin/v1/rooms/{id}/subrooms</c> — every sub-room of
+    /// a room with the settings that are adjustable per sub-room.
+    ///
+    /// Max players is genuinely per sub-room: the room's own
+    /// <see cref="RoomEntity.MaxCapacity"/> is what the room advertises and what
+    /// matchmaking hands to RoomInstance.MaxCapacity, while each sub-room caps
+    /// itself through <see cref="RoomSceneEntity.MaxPlayers"/>. In-game the
+    /// owner drives this from the "Max Player Count in This Subroom" slider
+    /// (PUT rooms/{id}/subrooms/{sub}/maxplayers); this is the same setting,
+    /// reachable for rooms an admin does not own.</summary>
+    [HttpGet("rooms/{id:long}/subrooms")]
+    public async Task<ActionResult> GetRoomSubRooms(long id)
+    {
+        if (!await db.Rooms.AnyAsync(r => r.Id == id)) return NotFound();
+
+        var scenes = await db.RoomScenes
+            .Where(s => s.RoomId == id)
+            .OrderBy(s => s.OrderIndex)
+            .ToListAsync();
+
+        return Ok(scenes.Select(s => new
+        {
+            // Ids go out as strings: the admin SPA is JavaScript and silently
+            // mangles integers past 2^53.
+            id = s.Id.ToString(),
+            subRoomId = s.OrderIndex,
+            name = s.Name,
+            maxPlayers = s.MaxPlayers,
+            canMatchmakeInto = s.CanMatchmakeInto,
+            isSandbox = s.IsSandbox,
+            dataBlobName = s.DataBlobName,
+            dataModifiedAt = s.DataModifiedAt,
+        }).ToList());
+    }
+
+    public sealed record SetSubRoomMaxPlayersRequest(int MaxPlayers);
+
+    /// <summary>PUT <c>api/admin/v1/rooms/{id}/subrooms/{subRoomId}/maxplayers</c>
+    /// — set one sub-room's player cap, addressed by its ORDER INDEX, which is
+    /// the sub-room id the client and the rest of the wire use (the row's own
+    /// primary key is an internal detail).
+    ///
+    /// Clamped to the same 1..80 range as the room-level capacity: 0 would make
+    /// a sub-room unjoinable, and the ceiling matches what the room props
+    /// endpoint already enforces so the two settings can't disagree about what
+    /// is a legal value.</summary>
+    [HttpPut("rooms/{id:long}/subrooms/{subRoomId:int}/maxplayers")]
+    [HttpPost("rooms/{id:long}/subrooms/{subRoomId:int}/maxplayers")]
+    public async Task<ActionResult> SetSubRoomMaxPlayers(
+        long id, int subRoomId, [FromBody] SetSubRoomMaxPlayersRequest body)
+    {
+        var room = await db.Rooms.FirstOrDefaultAsync(r => r.Id == id);
+        if (room is null) return NotFound();
+
+        var scene = await db.RoomScenes
+            .FirstOrDefaultAsync(s => s.RoomId == id && s.OrderIndex == subRoomId);
+        if (scene is null) return NotFound();
+
+        var previous = scene.MaxPlayers;
+        scene.MaxPlayers = Math.Clamp(body.MaxPlayers, 1, 80);
+        scene.DataModifiedAt = DateTime.UtcNow;
+        await db.SaveChangesAsync();
+
+        await LogAsync("update_subroom_maxplayers", "room", id,
+            $"subRoom={subRoomId} maxPlayers {previous} -> {scene.MaxPlayers}");
+
+        return Ok(new
+        {
+            id = scene.Id.ToString(),
+            subRoomId = scene.OrderIndex,
+            name = scene.Name,
+            maxPlayers = scene.MaxPlayers,
+        });
+    }
+
     public sealed record AddRoleRequest(long PlayerId, int Role, bool Accepted = true);
 
     /// <summary>POST <c>api/admin/v1/rooms/{id}/roles</c> — grant a
diff --git a/docs/admin.md b/docs/admin.md
index 96cadbb..22fc381 100644
--- a/docs/admin.md
+++ b/docs/admin.md
@@ -139,6 +139,46 @@ in S3 is modified. Toggle endpoint:
 `{"Disabled": bool}`. Clamped responses are served with a 60s edge TTL so
 flipping the toggle lands within a minute.
 
+## Per-sub-room max players (`/rooms` → room detail)
+
+Player caps are two separate settings, and conflating them is the easy
+mistake here:
+
+| Setting | Column | Scope |
+| --- | --- | --- |
+| `MaxCapacity` | `RoomEntity.MaxCapacity` | What the ROOM advertises; flows into `RoomInstance.MaxCapacity` for matchmaking and into the room-level `MaxPlayers` of the details payload. |
+| `MaxPlayers` | `RoomSceneEntity.MaxPlayers` | What ONE sub-room caps itself at; appears per entry in the details `SubRooms[]`. |
+
+The room-level figure must not be read off sub-room 0 — that collapses the
+two into one and makes an admin edit to a sub-room silently move the
+room's advertised capacity.
+
+Sub-room caps have two write paths onto the same column:
+
+- **In game** (room owner only) — the "Max Player Count in This Subroom"
+  slider issues `PUT rooms/{id}/subrooms/{sub}/maxplayers`. Unlike most of
+  its siblings this one does **not** form-encode: `NLDBPDCNNCF.MNBPCGJNLNP`
+  (`Int64, Int64, Int32`) builds a `BLNOGFGHIIF` whose single JSON key is
+  `maxPlayers`, with verb 3 = PUT. It reads the reply back as
+  `FGCPNAACHIK`, so the response is the full room-details shape and has to
+  carry the new value.
+- **Admin** (any room, ownership not required):
+  - `GET api/admin/v1/rooms/{id}/subrooms` — every sub-room with its cap,
+    matchmaking flag, sandbox flag and current data blob. Row ids go out as
+    **strings**; the SPA is JavaScript and mangles integers past 2^53.
+  - `PUT api/admin/v1/rooms/{id}/subrooms/{subRoomId}/maxplayers` with
+    `{"MaxPlayers": int}`. `subRoomId` is the sub-room's **order index** —
+    the id the client and the rest of the wire use — not the row's primary
+    key.
+
+Both paths clamp to 1..80, matching the room-level cap in
+`rooms/{id}/props`: 0 would make a sub-room unjoinable, and a shared range
+keeps the two settings from disagreeing about what is a legal value.
+
+Enforcement caveat carried over from `RoomEntity.MaxCapacity`: this is the
+advertised cap. The client never sets Photon `RoomOptions.MaxPlayers`, so
+hard enforcement still needs a ClientMod Photon patch.
+
 ## Build And Deploy
 
 The service Dockerfile builds the admin SPA for service images that need