diff --git a/packages/components/CHANGELOG.md b/packages/components/CHANGELOG.md
index acb59c743c81e8..fe326e847970b4 100644
--- a/packages/components/CHANGELOG.md
+++ b/packages/components/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### Deprecations
 
 -   `BoxControl`: Passive deprecate `onMouseOver`/`onMouseOut`. Pass to the `inputProps` prop instead ([#67332](https://github.com/WordPress/gutenberg/pull/67332)).
+-   `BoxControl`: Deprecate 36px default size ([#66704](https://github.com/WordPress/gutenberg/pull/66704)).
 
 ### Internal
 
diff --git a/packages/components/src/box-control/README.md b/packages/components/src/box-control/README.md
index ddadf938798ee9..8bcb5a5dad8fc2 100644
--- a/packages/components/src/box-control/README.md
+++ b/packages/components/src/box-control/README.md
@@ -21,6 +21,7 @@ function Example() {
 
   return (
     <BoxControl
+      __next40pxDefaultSize
       values={ values }
       onChange={ setValues }
     />
diff --git a/packages/components/src/box-control/index.tsx b/packages/components/src/box-control/index.tsx
index 7418fa19d74a0a..46cf2cd93a9444 100644
--- a/packages/components/src/box-control/index.tsx
+++ b/packages/components/src/box-control/index.tsx
@@ -33,6 +33,7 @@ import type {
 	BoxControlProps,
 	BoxControlValue,
 } from './types';
+import { maybeWarnDeprecated36pxSize } from '../utils/deprecated-36px-size';
 
 const defaultInputProps = {
 	min: 0,
@@ -64,6 +65,7 @@ function useUniqueId( idProp?: string ) {
  *
  *   return (
  *     <BoxControl
+ *       __next40pxDefaultSize
  *       values={ values }
  *       onChange={ setValues }
  *     />
@@ -155,6 +157,12 @@ function BoxControl( {
 		__next40pxDefaultSize,
 	};
 
+	maybeWarnDeprecated36pxSize( {
+		componentName: 'BoxControl',
+		__next40pxDefaultSize,
+		size: undefined,
+	} );
+
 	return (
 		<Grid
 			id={ id }
diff --git a/packages/components/src/box-control/stories/index.story.tsx b/packages/components/src/box-control/stories/index.story.tsx
index 783f9d047b1bb0..aa94e8c4bf00b8 100644
--- a/packages/components/src/box-control/stories/index.story.tsx
+++ b/packages/components/src/box-control/stories/index.story.tsx
@@ -49,6 +49,7 @@ const TemplateControlled: StoryFn< typeof BoxControl > = ( props ) => {
 export const Default = TemplateUncontrolled.bind( {} );
 Default.args = {
 	label: 'Label',
+	__next40pxDefaultSize: true,
 };
 
 export const Controlled = TemplateControlled.bind( {} );
diff --git a/packages/components/src/box-control/test/index.tsx b/packages/components/src/box-control/test/index.tsx
index 681e7721d0c13a..185a18b258951f 100644
--- a/packages/components/src/box-control/test/index.tsx
+++ b/packages/components/src/box-control/test/index.tsx
@@ -15,11 +15,14 @@ import { useState } from '@wordpress/element';
 import BoxControl from '..';
 import type { BoxControlProps, BoxControlValue } from '../types';
 
-const Example = ( extraProps: Omit< BoxControlProps, 'onChange' > ) => {
+const ControlledBoxControl = (
+	extraProps: Omit< BoxControlProps, 'onChange' >
+) => {
 	const [ state, setState ] = useState< BoxControlValue >();
 
 	return (
 		<BoxControl
+			__next40pxDefaultSize
 			values={ state }
 			onChange={ ( next ) => setState( next ) }
 			{ ...extraProps }
@@ -27,10 +30,17 @@ const Example = ( extraProps: Omit< BoxControlProps, 'onChange' > ) => {
 	);
 };
 
+const UncontrolledBoxControl = ( {
+	onChange = () => {},
+	...props
+}: Omit< BoxControlProps, 'onChange' > & {
+	onChange?: BoxControlProps[ 'onChange' ];
+} ) => <BoxControl __next40pxDefaultSize onChange={ onChange } { ...props } />;
+
 describe( 'BoxControl', () => {
 	describe( 'Basic rendering', () => {
 		it( 'should render a box control input', () => {
-			render( <BoxControl onChange={ () => {} } /> );
+			render( <UncontrolledBoxControl /> );
 
 			expect(
 				screen.getByRole( 'group', { name: 'Box Control' } )
@@ -43,7 +53,7 @@ describe( 'BoxControl', () => {
 		it( 'should update values when interacting with input', async () => {
 			const user = userEvent.setup();
 
-			render( <BoxControl onChange={ () => {} } /> );
+			render( <UncontrolledBoxControl /> );
 
 			const input = screen.getByRole( 'textbox', { name: 'All sides' } );
 
@@ -54,7 +64,7 @@ describe( 'BoxControl', () => {
 		} );
 
 		it( 'should update input values when interacting with slider', () => {
-			render( <BoxControl onChange={ () => {} } /> );
+			render( <UncontrolledBoxControl /> );
 
 			const slider = screen.getByRole( 'slider' );
 
@@ -68,7 +78,7 @@ describe( 'BoxControl', () => {
 
 		it( 'should update slider values when interacting with input', async () => {
 			const user = userEvent.setup();
-			render( <BoxControl onChange={ () => {} } /> );
+			render( <UncontrolledBoxControl /> );
 
 			const input = screen.getByRole( 'textbox', {
 				name: 'All sides',
@@ -82,7 +92,7 @@ describe( 'BoxControl', () => {
 		} );
 
 		it( 'should render the number input with a default min value of 0', () => {
-			render( <BoxControl onChange={ () => {} } /> );
+			render( <UncontrolledBoxControl /> );
 
 			const input = screen.getByRole( 'textbox', { name: 'All sides' } );
 
@@ -91,10 +101,7 @@ describe( 'BoxControl', () => {
 
 		it( 'should pass down `inputProps` to the underlying number input', () => {
 			render(
-				<BoxControl
-					onChange={ () => {} }
-					inputProps={ { min: 10, max: 50 } }
-				/>
+				<UncontrolledBoxControl inputProps={ { min: 10, max: 50 } } />
 			);
 
 			const input = screen.getByRole( 'textbox', { name: 'All sides' } );
@@ -108,7 +115,7 @@ describe( 'BoxControl', () => {
 		it( 'should reset values when clicking Reset', async () => {
 			const user = userEvent.setup();
 
-			render( <BoxControl onChange={ () => {} } /> );
+			render( <UncontrolledBoxControl /> );
 
 			const input = screen.getByRole( 'textbox', {
 				name: 'All sides',
@@ -127,7 +134,7 @@ describe( 'BoxControl', () => {
 		it( 'should reset values when clicking Reset, if controlled', async () => {
 			const user = userEvent.setup();
 
-			render( <Example /> );
+			render( <ControlledBoxControl /> );
 
 			const input = screen.getByRole( 'textbox', {
 				name: 'All sides',
@@ -146,7 +153,7 @@ describe( 'BoxControl', () => {
 		it( 'should reset values when clicking Reset, if controlled <-> uncontrolled state changes', async () => {
 			const user = userEvent.setup();
 
-			render( <Example /> );
+			render( <ControlledBoxControl /> );
 
 			const input = screen.getByRole( 'textbox', {
 				name: 'All sides',
@@ -166,7 +173,9 @@ describe( 'BoxControl', () => {
 			const user = userEvent.setup();
 			const spyChange = jest.fn();
 
-			render( <BoxControl onChange={ ( v ) => spyChange( v ) } /> );
+			render(
+				<UncontrolledBoxControl onChange={ ( v ) => spyChange( v ) } />
+			);
 
 			const input = screen.getByRole( 'textbox', {
 				name: 'All sides',
@@ -196,7 +205,7 @@ describe( 'BoxControl', () => {
 		it( 'should update a single side value when unlinked', async () => {
 			const user = userEvent.setup();
 
-			render( <Example /> );
+			render( <ControlledBoxControl /> );
 
 			await user.click(
 				screen.getByRole( 'button', { name: 'Unlink sides' } )
@@ -224,7 +233,7 @@ describe( 'BoxControl', () => {
 		it( 'should update a single side value when using slider unlinked', async () => {
 			const user = userEvent.setup();
 
-			render( <Example /> );
+			render( <ControlledBoxControl /> );
 
 			await user.click(
 				screen.getByRole( 'button', { name: 'Unlink sides' } )
@@ -252,7 +261,7 @@ describe( 'BoxControl', () => {
 		it( 'should update a whole axis when value is changed when unlinked', async () => {
 			const user = userEvent.setup();
 
-			render( <Example splitOnAxis /> );
+			render( <ControlledBoxControl splitOnAxis /> );
 
 			await user.click(
 				screen.getByRole( 'button', { name: 'Unlink sides' } )
@@ -276,7 +285,7 @@ describe( 'BoxControl', () => {
 		it( 'should update a whole axis using a slider when value is changed when unlinked', async () => {
 			const user = userEvent.setup();
 
-			render( <Example splitOnAxis /> );
+			render( <ControlledBoxControl splitOnAxis /> );
 
 			await user.click(
 				screen.getByRole( 'button', { name: 'Unlink sides' } )
@@ -300,7 +309,7 @@ describe( 'BoxControl', () => {
 		it( 'should show "Mixed" label when sides have different values but are linked', async () => {
 			const user = userEvent.setup();
 
-			render( <Example /> );
+			render( <ControlledBoxControl /> );
 
 			const unlinkButton = screen.getByRole( 'button', {
 				name: 'Unlink sides',
@@ -330,7 +339,7 @@ describe( 'BoxControl', () => {
 			const user = userEvent.setup();
 
 			// Render control.
-			render( <BoxControl onChange={ () => {} } /> );
+			render( <UncontrolledBoxControl /> );
 
 			// Make unit selection on all input control.
 			await user.selectOptions(
@@ -362,7 +371,7 @@ describe( 'BoxControl', () => {
 			const user = userEvent.setup();
 
 			// Render control.
-			const { rerender } = render( <BoxControl onChange={ () => {} } /> );
+			const { rerender } = render( <UncontrolledBoxControl /> );
 
 			// Make unit selection on all input control.
 			await user.selectOptions(
@@ -390,9 +399,7 @@ describe( 'BoxControl', () => {
 			} );
 
 			// Rerender with individual side value & confirm unit is selected.
-			rerender(
-				<BoxControl values={ { top: '2.5em' } } onChange={ () => {} } />
-			);
+			rerender( <UncontrolledBoxControl values={ { top: '2.5em' } } /> );
 
 			const rerenderedControls = screen.getAllByRole( 'combobox', {
 				name: 'Select unit',
@@ -414,7 +421,7 @@ describe( 'BoxControl', () => {
 			const user = userEvent.setup();
 			const onChangeSpy = jest.fn();
 
-			render( <BoxControl onChange={ onChangeSpy } /> );
+			render( <UncontrolledBoxControl onChange={ onChangeSpy } /> );
 
 			const valueInput = screen.getByRole( 'textbox', {
 				name: 'All sides',
@@ -443,7 +450,7 @@ describe( 'BoxControl', () => {
 			const user = userEvent.setup();
 			const setState = jest.fn();
 
-			render( <BoxControl onChange={ setState } /> );
+			render( <UncontrolledBoxControl onChange={ setState } /> );
 
 			await user.selectOptions(
 				screen.getByRole( 'combobox', {
diff --git a/packages/components/src/tools-panel/tools-panel/README.md b/packages/components/src/tools-panel/tools-panel/README.md
index 1daa7537335e1c..1895f5ccc843ec 100644
--- a/packages/components/src/tools-panel/tools-panel/README.md
+++ b/packages/components/src/tools-panel/tools-panel/README.md
@@ -124,6 +124,7 @@ export function DimensionPanel() {
 				onDeselect={ () => setPadding( undefined ) }
 			>
 				<BoxControl
+					__next40pxDefaultSize
 					label={ __( 'Padding' ) }
 					onChange={ setPadding }
 					values={ padding }
@@ -136,6 +137,7 @@ export function DimensionPanel() {
 				onDeselect={ () => setMargin( undefined ) }
 			>
 				<BoxControl
+					__next40pxDefaultSize
 					label={ __( 'Margin' ) }
 					onChange={ setMargin }
 					values={ margin }