How to resize an image on a Mac

To crop to an exact shape, such as a 1080 × 1350 Instagram post or a 1584 × 396 LinkedIn banner, use the browser resizer further down. It works in Safari and Chrome on any Mac.

Resize an image in Preview

1. Open the image in Preview (double-click it, or right-click and choose Open With > Preview).
2. Choose Tools > Adjust Size. You can also click the Markup button and then the Adjust Size button.
3. Enter new values for Width and Height, or choose a size from the Fit into menu.
4. To resize by a percentage, choose percent from the menu next to the Width and Height fields.
5. Leave Scale proportionally selected. Change one side and Preview works out the other.
6. Click OK, then choose File > Save, or File > Export to keep the original.

If you pick a size from Fit into, one side may come out smaller than the size you chose. That's Preview keeping the proportions.

Resize many images at once

Preview can resize a whole batch:

1. Select all the images in Finder and open them together, so they share one Preview window.
2. In that window's sidebar, select the images you want to change (press Command-A for all).
3. Choose Tools > Adjust Size and enter the new size.

Every selected image gets the same treatment. Work on copies if you want to keep the originals, because saving overwrites them.

Make the file smaller

To shrink an image's file size, for an email or an upload limit:

1. Choose Tools > Adjust Size and make sure Resample image is selected.
2. Enter a smaller value in Resolution, or smaller dimensions.
3. Check the new size shown at the bottom of the window, then click OK.

Exporting as JPG with the quality slider lower (File > Export) also cuts the file size a lot, especially for screenshots saved as PNG.

Change the size without losing detail

Apple notes a useful trick: untick Resample image before you change the width or height. Preview then changes the print size and resolution but keeps every pixel, so nothing is lost. Use it when a print shop asks for a size in inches or centimetres.

Resize for social media without guessing

Preview resizes, but it doesn't know what Instagram, LinkedIn or YouTube expect, and getting an exact shape means cropping by hand. The resizer below does both: pick a network and a size, or type your own width and height, and it crops or fits your image in one step.

It opens in fit mode, so the whole picture stays in the frame with a background colour around it. Switch to fill to crop to the shape instead, and move the crop sliders to choose which part stays. It runs in your browser, so the image never leaves your Mac. YouTube's own help even suggests Preview or an online resizer for banner images; this one has the 2560 × 1440 banner size built in.

Which to use

• Preview: quick resizes, batches, file size, print sizes. It's already on your Mac.
• The browser resizer: exact sizes for social networks, crop position, fit with a colour or blur, and every size for one network as a zip.

On an iPhone or iPad, the browser resizer works the same way in Safari.