diff --git a/docs/spec/canvas-pane.md b/docs/spec/canvas-pane.md
index 1eb1bb1..9cfaa58 100644
--- a/docs/spec/canvas-pane.md
+++ b/docs/spec/canvas-pane.md
@@ -55,6 +55,7 @@ A `SystemView` drives its own updates: the beads dashboard polls `/beads-data` e
 - The pane opens and closes from the header Canvas button and the `C` key.
 - Open or closed state persists in global config.
 - Position selector supports left, right, top, and bottom docking, and the selected position persists.
+- Size selector supports 1:1 (default) and 2:1 — at 2:1 the open pane takes two-thirds of the layout instead of half — and the selected size persists in global config.
 - The pane is scoped to the focused worktree. If that worktree has docs, the pane shows its active doc.
 - Worktrees with multiple docs show tab buttons. The active doc's tab always renders — a lone `AgentDoc` now gets a labeled tab (with a compact last-modified age) instead of a bare iframe, and a lone `SystemView` still shows its `.canvas-system-tab` entry so its beads-count badge stays visible. (See also `docs/spec/canvas-authoring-dx.md`.)
 - Selecting a tab marks that doc viewed.
diff --git a/src/Client/App.fs b/src/Client/App.fs
index 82de6cf..0d6a519 100644
--- a/src/Client/App.fs
+++ b/src/Client/App.fs
@@ -180,6 +180,7 @@ let update msg model =
                     { model.Canvas with
                         CanvasPaneOpen = if isFirstLoad then response.CanvasPaneOpen else model.Canvas.CanvasPaneOpen
                         CanvasPosition = if isFirstLoad then response.CanvasPosition else model.Canvas.CanvasPosition
+                        CanvasSize = if isFirstLoad then response.CanvasSize else model.Canvas.CanvasSize
                         PreviousCanvasHashes = currentCanvasHashes
                         CanvasEvents = canvasEvents
                         CanvasSendState = canvasSendState } }
@@ -465,6 +466,8 @@ let update msg model =
 
     | SetCanvasPosition position -> CanvasUpdate.setCanvasPosition position model
 
+    | SetCanvasSize size -> CanvasUpdate.setCanvasSize size model
+
     | SelectCanvasDoc (scopedKey, filename) -> CanvasUpdate.selectCanvasDoc scopedKey filename model
 
     | FocusOverviewCard scopedKey ->
@@ -696,6 +699,11 @@ let view model dispatch =
         | CanvasPosition.Top -> "canvas-top"
         | CanvasPosition.Bottom -> "canvas-bottom"
 
+    let canvasSizeClass =
+        match model.Canvas.CanvasSize with
+        | CanvasSize.Ratio1To1 -> "canvas-size-1to1"
+        | CanvasSize.Ratio2To1 -> "canvas-size-2to1"
+
     let dashboardClass =
         match model.Canvas.CanvasPaneOpen with
         | true -> $"dashboard canvas-open {canvasPositionClass}"
@@ -703,7 +711,7 @@ let view model dispatch =
 
     let layoutClass =
         match model.Canvas.CanvasPaneOpen with
-        | true -> $"app-layout canvas-open {canvasPositionClass}"
+        | true -> $"app-layout canvas-open {canvasPositionClass} {canvasSizeClass}"
         | false -> "app-layout"
 
     let cardProps: CardViewProps =
diff --git a/src/Client/AppTypes.fs b/src/Client/AppTypes.fs
index b2e3e6e..9039302 100644
--- a/src/Client/AppTypes.fs
+++ b/src/Client/AppTypes.fs
@@ -70,6 +70,7 @@ type Msg =
     | UserActivity of now: float
     | ToggleCanvasPane
     | SetCanvasPosition of CanvasPosition
+    | SetCanvasSize of CanvasSize
     | SelectCanvasDoc of scopedKey: string * filename: string
     | FocusOverviewCard of scopedKey: string
     | OpenCanvasDoc of scopedKey: string * filename: string
diff --git a/src/Client/CanvasPane.fs b/src/Client/CanvasPane.fs
index f818cc0..2e6fca5 100644
--- a/src/Client/CanvasPane.fs
+++ b/src/Client/CanvasPane.fs
@@ -146,6 +146,7 @@ let private overviewView (repos: RepoModel list) (bridgeLiveness: Map<string, Br
 /// silent argument transposition compile and surface only at runtime.
 type CanvasPaneCallbacks =
     { SetPosition: CanvasPosition -> unit
+      SetSize: CanvasSize -> unit
       SelectDoc: string -> unit
       OnOverviewClick: string -> unit
       OnOverviewDocClick: string -> string -> unit
@@ -154,8 +155,9 @@ type CanvasPaneCallbacks =
       DismissDocError: unit -> unit
       LaunchSession: unit -> unit }
 
-let view (isOpen: bool) (position: CanvasPosition) (focusedDoc: (WorktreeStatus * CanvasDoc) option) (allRepos: RepoModel list) (sendState: CanvasSendState) (docError: DocJsError option) (bridgeLiveness: Map<string, BridgeLiveness>) (unviewedFilenames: Set<string>) (visitedDocs: string list) (callbacks: CanvasPaneCallbacks) =
+let view (isOpen: bool) (position: CanvasPosition) (size: CanvasSize) (focusedDoc: (WorktreeStatus * CanvasDoc) option) (allRepos: RepoModel list) (sendState: CanvasSendState) (docError: DocJsError option) (bridgeLiveness: Map<string, BridgeLiveness>) (unviewedFilenames: Set<string>) (visitedDocs: string list) (callbacks: CanvasPaneCallbacks) =
     let { SetPosition = setPosition
+          SetSize = setSize
           SelectDoc = selectDoc
           OnOverviewClick = onOverviewClick
           OnOverviewDocClick = onOverviewDocClick
@@ -163,14 +165,17 @@ let view (isOpen: bool) (position: CanvasPosition) (focusedDoc: (WorktreeStatus
           DismissError = dismissError
           DismissDocError = dismissDocError
           LaunchSession = launchSession } = callbacks
-    let positionButton (canvasPosition: CanvasPosition) (label: string) (title: string) =
+    let toggleButton (baseClass: string) (isActive: bool) (onClick: unit -> unit) (label: string) (title: string) =
         Html.button [
-            prop.className (if canvasPosition = position then "canvas-pos-btn active" else "canvas-pos-btn")
-            prop.onClick (fun _ -> setPosition canvasPosition)
+            prop.className (if isActive then $"{baseClass} active" else baseClass)
+            prop.onClick (fun _ -> onClick ())
             prop.title title
             prop.text label
         ]
 
+    let positionButton (canvasPosition: CanvasPosition) label title =
+        toggleButton "canvas-pos-btn" (canvasPosition = position) (fun () -> setPosition canvasPosition) label title
+
     let positionButtons =
         Html.div [
             prop.className "canvas-pos-group"
@@ -182,6 +187,18 @@ let view (isOpen: bool) (position: CanvasPosition) (focusedDoc: (WorktreeStatus
             ]
         ]
 
+    let sizeButton (canvasSize: CanvasSize) label title =
+        toggleButton "canvas-size-btn" (canvasSize = size) (fun () -> setSize canvasSize) label title
+
+    let sizeButtons =
+        Html.div [
+            prop.className "canvas-size-group"
+            prop.children [
+                sizeButton CanvasSize.Ratio1To1 "1:1" "Canvas same size as dashboard"
+                sizeButton CanvasSize.Ratio2To1 "2:1" "Make the canvas twice the size of the dashboard"
+            ]
+        ]
+
     let headerBar (tabs: Fable.React.ReactElement list) (activeDoc: CanvasDoc option) (showLaunchBtn: bool) =
         Html.div [
             prop.className "canvas-tab-bar"
@@ -209,6 +226,7 @@ let view (isOpen: bool) (position: CanvasPosition) (focusedDoc: (WorktreeStatus
                                 prop.children [ ArchiveViews.archiveIcon ]
                             ]
                         | _ -> ()
+                        sizeButtons
                         positionButtons
                     ]
                 ]
diff --git a/src/Client/CanvasState.fs b/src/Client/CanvasState.fs
index 529decf..5cfe19c 100644
--- a/src/Client/CanvasState.fs
+++ b/src/Client/CanvasState.fs
@@ -12,6 +12,7 @@ open Elmish
 type CanvasState =
     { CanvasPaneOpen: bool
       CanvasPosition: CanvasPosition
+      CanvasSize: CanvasSize
       ActiveCanvasDoc: Map<string, string>
       VisitedCanvasDocs: Map<string, string list>
       LastViewedHashes: Map<string, Map<string, string>>
@@ -33,6 +34,7 @@ type CanvasState =
 let empty : CanvasState =
     { CanvasPaneOpen = false
       CanvasPosition = CanvasPosition.Right
+      CanvasSize = CanvasSize.Ratio1To1
       ActiveCanvasDoc = Map.empty
       VisitedCanvasDocs = Map.empty
       LastViewedHashes = Map.empty
diff --git a/src/Client/CanvasUpdate.fs b/src/Client/CanvasUpdate.fs
index 58b98be..fe7a1c4 100644
--- a/src/Client/CanvasUpdate.fs
+++ b/src/Client/CanvasUpdate.fs
@@ -55,6 +55,10 @@ let setCanvasPosition (position: CanvasPosition) (model: Model) =
     { model with Canvas = { model.Canvas with CanvasPosition = position } },
     Cmd.OfAsync.attempt worktreeApi.Value.saveCanvasPosition position (fun _ -> NoOp)
 
+let setCanvasSize (size: CanvasSize) (model: Model) =
+    { model with Canvas = { model.Canvas with CanvasSize = size } },
+    Cmd.OfAsync.attempt worktreeApi.Value.saveCanvasSize size (fun _ -> NoOp)
+
 let selectCanvasDoc (scopedKey: string) (filename: string) (model: Model) =
     let wasAlreadyVisited =
         model.Canvas.VisitedCanvasDocs
diff --git a/src/Client/CanvasView.fs b/src/Client/CanvasView.fs
index 54b08dd..2394629 100644
--- a/src/Client/CanvasView.fs
+++ b/src/Client/CanvasView.fs
@@ -66,6 +66,7 @@ let view (model: Model) (dispatch: Dispatch<Msg>) =
 
     let canvasCallbacks: CanvasPane.CanvasPaneCallbacks =
         { SetPosition = SetCanvasPosition >> dispatch
+          SetSize = SetCanvasSize >> dispatch
           SelectDoc = selectCanvasDoc
           OnOverviewClick = onOverviewClick
           OnOverviewDocClick = onOverviewDocClick
@@ -74,4 +75,4 @@ let view (model: Model) (dispatch: Dispatch<Msg>) =
           DismissDocError = (fun () -> dispatch DismissCanvasDocError)
           LaunchSession = launchCanvasSession }
 
-    CanvasPane.view model.Canvas.CanvasPaneOpen model.Canvas.CanvasPosition (focusedWorktreeCanvasDoc model) model.Repos model.Canvas.CanvasSendState model.Canvas.DocError model.Canvas.BridgeLiveness focusedUnviewedFilenames focusedVisitedDocs canvasCallbacks
+    CanvasPane.view model.Canvas.CanvasPaneOpen model.Canvas.CanvasPosition model.Canvas.CanvasSize (focusedWorktreeCanvasDoc model) model.Repos model.Canvas.CanvasSendState model.Canvas.DocError model.Canvas.BridgeLiveness focusedUnviewedFilenames focusedVisitedDocs canvasCallbacks
diff --git a/src/Client/index.html b/src/Client/index.html
index 9a2b7d3..1d7b8a0 100644
--- a/src/Client/index.html
+++ b/src/Client/index.html
@@ -462,6 +462,12 @@
         .app-layout.canvas-bottom > .canvas-pane.open {
             flex: 0 0 50%;
         }
+        .app-layout.canvas-size-2to1.canvas-left > .canvas-pane.open,
+        .app-layout.canvas-size-2to1.canvas-right > .canvas-pane.open,
+        .app-layout.canvas-size-2to1.canvas-top > .canvas-pane.open,
+        .app-layout.canvas-size-2to1.canvas-bottom > .canvas-pane.open {
+            flex: 0 0 66.667%;
+        }
         .app-layout.canvas-right > .canvas-pane { border-left: 1px solid #313244; }
         .app-layout.canvas-left > .canvas-pane { border-right: 1px solid #313244; }
         .app-layout.canvas-top > .canvas-pane { border-bottom: 1px solid #313244; }
@@ -482,7 +488,7 @@
             flex: 1;
             min-width: 0;
         }
-        .canvas-pos-group {
+        .canvas-pos-group, .canvas-size-group {
             display: flex;
             gap: 4px;
             flex-shrink: 0;
@@ -513,15 +519,15 @@
             opacity: 0.6;
         }
         .canvas-launch-btn:hover { color: #a6e3a1; border-color: #a6e3a1; opacity: 1; }
-        .canvas-pos-btn {
+        .canvas-pos-btn, .canvas-size-btn {
             background: #313244; border: 1px solid #45475a; border-radius: 4px;
             padding: 2px 8px; font-size: 0.85em; cursor: pointer; color: #bac2de;
             font-family: inherit; transition: background 0.15s, border-color 0.15s, opacity 0.15s;
             line-height: 1.4; opacity: 0.4;
         }
-        .canvas-pos-btn:hover { background: #45475a; border-color: #585b70; opacity: 1; }
-        .canvas-pos-btn.active { background: #2e3452; border-color: #89b4fa; color: #89b4fa; opacity: 0.4; }
-        .canvas-pos-btn.active:hover { opacity: 1; }
+        .canvas-pos-btn:hover, .canvas-size-btn:hover { background: #45475a; border-color: #585b70; opacity: 1; }
+        .canvas-pos-btn.active, .canvas-size-btn.active { background: #2e3452; border-color: #89b4fa; color: #89b4fa; opacity: 0.4; }
+        .canvas-pos-btn.active:hover, .canvas-size-btn.active:hover { opacity: 1; }
         .canvas-error-banner {
             display: flex; align-items: center; justify-content: space-between;
             background: #3a1e2a; color: #f38ba8; padding: 4px 12px;
diff --git a/src/Server/DemoFixture.fs b/src/Server/DemoFixture.fs
index c15770a..887d2b0 100644
--- a/src/Server/DemoFixture.fs
+++ b/src/Server/DemoFixture.fs
@@ -358,7 +358,8 @@ let private baseDashboard: DashboardResponse =
       EditorName = "VS Code"
       CollapsedRepos = Set.empty
       CanvasPaneOpen = false
-      CanvasPosition = CanvasPosition.Right }
+      CanvasPosition = CanvasPosition.Right
+      CanvasSize = CanvasSize.Ratio1To1 }
 
 let private baseFixture: FixtureData =
     { Worktrees = baseDashboard
diff --git a/src/Server/WorktreeApi.fs b/src/Server/WorktreeApi.fs
index b47d3a3..12d09fc 100644
--- a/src/Server/WorktreeApi.fs
+++ b/src/Server/WorktreeApi.fs
@@ -62,6 +62,7 @@ let readOnlyApi
       saveCollapsedRepos = fun _ -> async { return () }
       saveCanvasPaneOpen = fun _ -> async { return () }
       saveCanvasPosition = fun _ -> async { return () }
+      saveCanvasSize = fun _ -> async { return () }
       resumeSession = fun _ -> async { return Error $"Session management is not available in {modeName}" }
       sendCanvasMessage = fun _ -> async { return CanvasMessageResult.Queued }
       archiveCanvasDoc = fun _ -> async { return Error $"Archive canvas doc is not available in {modeName}" }
@@ -394,6 +395,22 @@ let private writeCanvasPosition (position: CanvasPosition) =
         | CanvasPosition.Bottom -> "bottom"
     updateGlobalConfig "canvas position" [ "canvasPosition", System.Text.Json.Nodes.JsonValue.Create(value) :> System.Text.Json.Nodes.JsonNode ]
 
+let private readCanvasSize () : CanvasSize =
+    withConfigDocument CanvasSize.Ratio1To1 (fun root ->
+        match root.TryGetProperty("canvasSize") with
+        | true, prop when prop.ValueKind = System.Text.Json.JsonValueKind.String ->
+            match prop.GetString() with
+            | "2to1" -> CanvasSize.Ratio2To1
+            | _ -> CanvasSize.Ratio1To1
+        | _ -> CanvasSize.Ratio1To1)
+
+let private writeCanvasSize (size: CanvasSize) =
+    let value =
+        match size with
+        | CanvasSize.Ratio1To1 -> "1to1"
+        | CanvasSize.Ratio2To1 -> "2to1"
+    updateGlobalConfig "canvas size" [ "canvasSize", System.Text.Json.Nodes.JsonValue.Create(value) :> System.Text.Json.Nodes.JsonNode ]
+
 let private readLastViewedHashes () : Map<string, Map<string, string>> =
     withConfigDocument Map.empty (fun root ->
         match root.TryGetProperty("lastViewedHashes") with
@@ -481,7 +498,8 @@ let getWorktrees
               EditorName = getEditorConfig () |> snd
               CollapsedRepos = readCollapsedRepos ()
               CanvasPaneOpen = readCanvasPaneOpen ()
-              CanvasPosition = readCanvasPosition () }
+              CanvasPosition = readCanvasPosition ()
+              CanvasSize = readCanvasSize () }
     }
 
 let private openEditor (validatePath: string -> Async<bool>) (wtPath: WorktreePath) =
@@ -615,7 +633,7 @@ let worktreeApi
     | Some f ->
         { readOnlyApi
             "fixture mode"
-            (fun () -> async { return { f.Worktrees with DeployBranch = None; SystemMetrics = None; EditorName = getEditorConfig () |> snd; CollapsedRepos = readCollapsedRepos (); CanvasPaneOpen = false; CanvasPosition = CanvasPosition.Right } })
+            (fun () -> async { return { f.Worktrees with DeployBranch = None; SystemMetrics = None; EditorName = getEditorConfig () |> snd; CollapsedRepos = readCollapsedRepos (); CanvasPaneOpen = false; CanvasPosition = CanvasPosition.Right; CanvasSize = CanvasSize.Ratio1To1 } })
             (fun () -> async { return f.SyncStatus })
           with
             getBranches = fun _ -> async { return [ "main"; "develop"; "feature/sample" ] }
@@ -787,6 +805,7 @@ let worktreeApi
           saveCollapsedRepos = fun repos -> async { writeCollapsedRepos repos }
           saveCanvasPaneOpen = fun isOpen -> async { writeCanvasPaneOpen isOpen }
           saveCanvasPosition = fun pos -> async { writeCanvasPosition pos }
+          saveCanvasSize = fun size -> async { writeCanvasSize size }
           resumeSession = fun wtPath ->
               withValidatedPath wtPath "resumeSession" (fun () ->
                   async {
diff --git a/src/Shared/Types.fs b/src/Shared/Types.fs
index 879205d..39841c4 100644
--- a/src/Shared/Types.fs
+++ b/src/Shared/Types.fs
@@ -97,6 +97,14 @@ type CanvasPosition =
     | Top
     | Bottom
 
+/// Relative size of the canvas pane vs the dashboard when the pane is open.
+/// Ratio1To1 (default) splits the layout evenly; Ratio2To1 gives the canvas
+/// twice the dashboard's share.
+[<RequireQualifiedAccess>]
+type CanvasSize =
+    | Ratio1To1
+    | Ratio2To1
+
 type CanvasDocKind =
     | AgentDoc      // authored & owned by a session; interactive; file-driven
     | SystemView    // server-generated; data-driven; no owner (e.g. the beads dashboard)
@@ -239,7 +247,8 @@ type DashboardResponse =
       EditorName: string
       CollapsedRepos: Set<RepoId>
       CanvasPaneOpen: bool
-      CanvasPosition: CanvasPosition }
+      CanvasPosition: CanvasPosition
+      CanvasSize: CanvasSize }
 
 type FixtureData =
     { Worktrees: DashboardResponse
@@ -270,6 +279,7 @@ type IWorktreeApi =
       saveCollapsedRepos: RepoId list -> Async<unit>
       saveCanvasPaneOpen: bool -> Async<unit>
       saveCanvasPosition: CanvasPosition -> Async<unit>
+      saveCanvasSize: CanvasSize -> Async<unit>
       resumeSession: WorktreePath -> Async<Result<unit, string>>
       sendCanvasMessage: CanvasMessageRequest -> Async<CanvasMessageResult>
       archiveCanvasDoc: ArchiveCanvasDocRequest -> Async<Result<unit, string>>
diff --git a/src/Tests/ArchiveTests.fs b/src/Tests/ArchiveTests.fs
index 618f832..9797e00 100644
--- a/src/Tests/ArchiveTests.fs
+++ b/src/Tests/ArchiveTests.fs
@@ -359,7 +359,7 @@ type ArchiveE2ETests() =
 
     let makeDashboardJson (worktrees: string list) =
         let wts = worktrees |> String.concat ","
-        $"""{{"Repos":[{{"RepoId":{{"RepoId":"TestRepo"}},"RootFolderName":"TestRepo","Worktrees":[{wts}],"IsReady":true,"BaseBranch":"main"}}],"SchedulerEvents":[],"LatestByCategory":{{}},"AppVersion":"test","EditorName":"","CollapsedRepos":[],"CanvasPaneOpen":false,"CanvasPosition":"Right"}}"""
+        $"""{{"Repos":[{{"RepoId":{{"RepoId":"TestRepo"}},"RootFolderName":"TestRepo","Worktrees":[{wts}],"IsReady":true,"BaseBranch":"main"}}],"SchedulerEvents":[],"LatestByCategory":{{}},"AppVersion":"test","EditorName":"","CollapsedRepos":[],"CanvasPaneOpen":false,"CanvasPosition":"Right","CanvasSize":"Ratio1To1"}}"""
 
     let emptySyncStatus = "{}"