Share pictures faster and better by making them smaller: find out here how to resize an image in Preview swiftly for free on a Mac using macOS or OS X.

First, Feeling Underpromoted?

Ask the measly pawn on the chess board. Instead of becoming a queen when it reached the boar’s foreign end, it was promoted—ahem—underpromoted to a mere knight!

This is no nightmare, though: if underpromotion happens in chess, then because it was the better choice. Just like undersizing an image can be the best choice—when you want to include it in an email signature, for instance.

How to Resize an Image in Preview on a Mac

To change the size of an image with the Preview application that comes with any Mac‘s macOS:

  1. Open the image in Preview.

    Tip: To make sure the picture opens in Preview, click on the image with the right mouse button and select Open With | Preview from the context menu.Open the image in Preview

  2. Select Tools | Adjust Size… from the menu.

    Tip: See below for setting up a keyboard shortcut for resizing.Select

  3. Check both Scale proportionally and Resample image.

    Note: These options ensure the image looks good at the reduced size and, to some degree, if you enlarge it, too.Check both

  4. Now select pixels under Width: and Height:.

  5. Enter the maximum width under Width: or the maximum height under Height:.

    Note: The other dimension will change automatically. Watch it. If it exceeds your desired maximum, enter the maximum size under that dimension.
    Example: You want the image for your signature to be 100 pixels wide as a maximum and no more than 85 pixels high. The image is currently 900 x 1348 pixels. After entering “100” under Width:Height: has changed to 150. That is too large, so you enter “85” under Height:. The dimensions are now 57 x 85 pixels.Enter the maximum width under

  6. Click OK.

  7. Press Command S to save the image.

    Tip: After uploading or using your image, you can restore the original resolution easily in Preview by pressing Command Z or selecting Edit | Undo Size Change from the menu.
    Alternative: Instead of undoing the size change, you can also save a copy: hold down the Option key while the File menu is open to reveal and use the Save As… command, which will let you save the image’s current state under a new name without changing the original. The keyboard shortcut for Save As… is Command Shift Option S.

How to Resize an Image in Preview on a Mac: FAQ

Is there a keyboard shortcut for Resizing an Image in Preview?

While there is no standard shortcut defined, you can create a keyboard shortcut for “Adjust Size…” in Preview, say Command Control S.

(How to resize an image in Preview on a Mac tested with macOS Mojave 10.14 and macOS High Sierra 10.13; updated August 2019; title image: StockUnlimited)