How to change canvas size in Photoshop on Mac: step by step for Photoshop 27.6

Canvas Size changes the frame around your picture. It does not scale the picture. Use it when you need more room on one side, a border around the edge, or a smaller frame that trims the edges. If you only need a smaller file, this is the wrong command.

Canvas size vs Image Size in Photoshop on Mac

The command sits in the Image menu, close to Image Size. The two names sound alike, but they do different jobs. Canvas Size changes the workspace. The pixels inside the picture keep their size, and new space appears around them. Image Size changes the pixels themselves, so the photo gets bigger or smaller.

Use Canvas Size when the photo is right and the frame is wrong. Use Image Size when the photo itself must change size. If you are unsure, look at the edges before you save. Stretched faces or squashed products tell you that you picked the wrong command.

Canvas extension color greyed out: check the Background layer

Photoshop treats the Background layer differently from other layers. Open Window > Layers to see the stack. A Background layer has a small lock icon and sits at the bottom of the stack.

The lock matters in two cases. A missing Background layer can grey out the extension color option. A locked Background also blocks a transparent border, because the new area needs an unlocked layer to show transparency. Check this first, and the rest of the steps go smoothly.

The Canvas Size dialog, field by field

The dialog is short. Five parts control the result. Learn what each one does, and the command stops feeling like guesswork.

• Unit dropdown: Percent, Pixels, Centimeters or Millimeters. Choose this first.
• Width and Height: the final size, unless Relative is ticked.
• Relative checkbox: unticked by default. Ticked, it adds or subtracts a set amount.
• Anchor grid: nine squares. The square you pick sets where the image sits.
• Canvas extension color: White by default, plus Grey, Black and Other.

Canvas Size does not preview anything. You type, click OK, and then check. That is why a quick undo is part of the normal workflow. If you want to see the result before you commit, the Crop tool is the better option.

Worked example: room for a headline on one side

Say you have a portrait and want clean space on the right for a headline. Open Canvas Size. Leave Relative unticked, then type a width larger than the current width. Keep the height the same.

Now click the middle-left square in the anchor grid. The photo stays on the left, and all the new width lands on the right. Keep White as the extension color, then click OK. Check the edge before you add any text.

Keep the headline on its own text layer, so you can move it without touching the photo.

Transparent border in Photoshop on Mac, not a solid color

A transparent border helps with logos, stickers and images for web pages with a colored background. Start by clearing the lock on the Background layer. Click its lock icon in the Layers panel. Then run Canvas Size and choose the new size.

The new area shows a checkerboard pattern. That pattern means transparent, not white. Save as PNG if you want to keep the transparency. JPEG cannot keep transparency, so the border gets a solid color.

Fill the new area with color or generated content

For a plain color fill, pick a color in Canvas Size. For a fill after the fact, use the Paint Bucket tool on the new area. The Paint Bucket needs a layer that accepts paint, so a locked Background gets in the way. Click the lock icon first, the same step that makes transparency possible.

The Crop tool offers three fill options: Default, Content-Aware Fill and Generative Expand. Content-Aware Fill builds the new area from nearby pixels. Generative Expand uses generative AI to extend the scene. If the Crop tool gives odd patches, Content-Aware is selected. Deselect it in the options bar.

Crop tool as an alternative to Canvas Size

Press C to choose the Crop tool. Drag the handles outside the image to extend the canvas. The Crop tool previews the result before you commit. It can extend one side more than another, so check every edge before you press Return.

Pick a unit for print or screen before you type

Decide the unit before you type anything. Pixels suit screens, because a screen has a fixed pixel size. Centimeters or Millimeters suit a print with a set size. Percent scales from the current frame, so it works well for quick, proportional changes.

Clipped pixels when you shrink the canvas

Shrinking the canvas cuts away the edges. Photoshop warns you first, with Proceed, Learn More and Cancel. Choose Cancel if you are not sure what gets lost. Save a copy of the file before you shrink it.

If you might need the cut edges later, use the Crop tool and untick Delete Cropped Pixels in the options bar. The cropped pixels stay in the file outside the visible frame, so you can bring them back.

Shortcut confusion: Option+Command+C or Shift+Command+C?

Most guides give Option+Command+C for Canvas Size on Mac. One guide, updated in September 2022, gives Shift+Command+C. The two conflict. Adobe's own shortcut page could not be checked for this page, so treat both as unconfirmed.

The safest route is the menu. Open the Image menu and read the shortcut printed next to Canvas Size in your copy of Photoshop. Use the printed shortcut, because menus can change between builds.

Photoshop on the web: canvas size options

The web app is a separate tool with fewer controls. Adobe's free online Photoshop page describes uploads of JPEG, JPG or PNG files up to 40MB. Files can be no larger than 8,000 by 8,000 pixels, and you upload one file at a time. The page does not describe canvas or image size controls.

An Adobe Community answer from November 2023 says there is no dedicated Canvas Size command on the web. It suggests the Crop tool under Size & position. Drag the crop handles outside the image, or type width and height values. That answer is user-written, so check the menus in your browser first.

Which version of Photoshop you need

Adobe's release coverage says Photoshop 27.0 came out on October 28, 2025. Photoshop 27.6 followed on April 28, 2026. Both need macOS 14.0 or later. If you are not sure which build you have, check your Photoshop version.

The steps on this page come from third-party guides. Adobe's own help pages could not be checked for this page. The main guide was written from Photoshop CC on Windows, and its sources did not show a Mac-specific change to the dialog. The screenshots may look a little different on your Mac, so the fields and the anchor grid are the parts to watch.

Common mistakes that waste time

One common mistake is using Image Size by accident. Another is choosing the wrong anchor square. A third is picking a unit you did not mean. A value typed in Percent makes a very different frame than the same number typed in Pixels.

Another mistake is trusting the first look. Canvas Size gives no preview, so check the result right after OK. Undo at once if an edge looks wrong. Stacking more changes on a bad frame makes the file harder to fix.

Edge cases when the file has several layers

Canvas Size applies to the whole document. Every layer gets the new frame, and its position stays tied to the anchor you chose. Check text, logos and shapes near the edges, because they can end up closer to the new border than you expect.

What to do next

Save a copy before you change the canvas on an important file. Use File > Save As, so the original keeps its size. If your menus differ from these steps, update Photoshop first, then try again.

For a daily Photoshop routine on Mac, the Photoshop page for designers covers shortcuts and a typical workflow.