diff --git a/packages/edit-site/src/components/layout/index.js b/packages/edit-site/src/components/layout/index.js
index 17c660b94f0036..1a1c2f3a3830a2 100644
--- a/packages/edit-site/src/components/layout/index.js
+++ b/packages/edit-site/src/components/layout/index.js
@@ -340,6 +340,12 @@ export default function Layout() {
 														! isEditorLoading
 													}
 													isFullWidth={ isEditing }
+													defaultSize={ {
+														width:
+															canvasSize.width -
+															24 /* $canvas-padding */,
+														height: canvasSize.height,
+													} }
 													isOversized={
 														isResizableFrameOversized
 													}
diff --git a/packages/edit-site/src/components/resizable-frame/index.js b/packages/edit-site/src/components/resizable-frame/index.js
index 2b98e46a71532e..ee5c98da09033f 100644
--- a/packages/edit-site/src/components/resizable-frame/index.js
+++ b/packages/edit-site/src/components/resizable-frame/index.js
@@ -6,7 +6,7 @@ import classnames from 'classnames';
 /**
  * WordPress dependencies
  */
-import { useState, useRef, useEffect } from '@wordpress/element';
+import { useState, useRef } from '@wordpress/element';
 import {
 	ResizableBox,
 	Tooltip,
@@ -82,6 +82,8 @@ function ResizableFrame( {
 	setIsOversized,
 	isReady,
 	children,
+	/** The default (unresized) width/height of the frame, based on the space availalbe in the viewport. */
+	defaultSize,
 	innerContentStyle,
 } ) {
 	const [ frameSize, setFrameSize ] = useState( INITIAL_FRAME_SIZE );
@@ -95,22 +97,13 @@ function ResizableFrame( {
 		[]
 	);
 	const { setCanvasMode } = unlock( useDispatch( editSiteStore ) );
-	const initialAspectRatioRef = useRef( null );
-	// The width of the resizable frame on initial render.
-	const initialComputedWidthRef = useRef( null );
 	const FRAME_TRANSITION = { type: 'tween', duration: isResizing ? 0 : 0.5 };
 	const frameRef = useRef( null );
 	const resizableHandleHelpId = useInstanceId(
 		ResizableFrame,
 		'edit-site-resizable-frame-handle-help'
 	);
-
-	// Remember frame dimensions on initial render.
-	useEffect( () => {
-		const { offsetWidth, offsetHeight } = frameRef.current.resizable;
-		initialComputedWidthRef.current = offsetWidth;
-		initialAspectRatioRef.current = offsetWidth / offsetHeight;
-	}, [] );
+	const defaultAspectRatio = defaultSize.width / defaultSize.height;
 
 	const handleResizeStart = ( _event, _direction, ref ) => {
 		// Remember the starting width so we don't have to get `ref.offsetWidth` on
@@ -126,7 +119,7 @@ function ResizableFrame( {
 		const maxDoubledDelta =
 			delta.width < 0 // is shrinking
 				? deltaAbs
-				: ( initialComputedWidthRef.current - startingWidth ) / 2;
+				: ( defaultSize.width - startingWidth ) / 2;
 		const deltaToDouble = Math.min( deltaAbs, maxDoubledDelta );
 		const doubleSegment = deltaAbs === 0 ? 0 : deltaToDouble / deltaAbs;
 		const singleSegment = 1 - doubleSegment;
@@ -135,17 +128,14 @@ function ResizableFrame( {
 
 		const updatedWidth = startingWidth + delta.width;
 
-		setIsOversized( updatedWidth > initialComputedWidthRef.current );
+		setIsOversized( updatedWidth > defaultSize.width );
 
 		// Width will be controlled by the library (via `resizeRatio`),
 		// so we only need to update the height.
 		setFrameSize( {
 			height: isOversized
 				? '100%'
-				: calculateNewHeight(
-						updatedWidth,
-						initialAspectRatioRef.current
-				  ),
+				: calculateNewHeight( updatedWidth, defaultAspectRatio ),
 		} );
 	};
 
@@ -186,15 +176,12 @@ function ResizableFrame( {
 				FRAME_MIN_WIDTH,
 				frameRef.current.resizable.offsetWidth + delta
 			),
-			initialComputedWidthRef.current
+			defaultSize.width
 		);
 
 		setFrameSize( {
 			width: newWidth,
-			height: calculateNewHeight(
-				newWidth,
-				initialAspectRatioRef.current
-			),
+			height: calculateNewHeight( newWidth, defaultAspectRatio ),
 		} );
 	};
 
@@ -291,9 +278,7 @@ function ResizableFrame( {
 									undefined
 								}
 								aria-valuemin={ FRAME_MIN_WIDTH }
-								aria-valuemax={
-									initialComputedWidthRef.current
-								}
+								aria-valuemax={ defaultSize.width }
 								onKeyDown={ handleResizableHandleKeyDown }
 								initial="hidden"
 								exit="hidden"