Share pictures faster and better by making them smaller: find out here how to resize an image on a Mac swiftly and for free using Preview (using JPEG, PNG; GIF, HEIF, and many picture formats more).
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 with Mac Preview (GIF, PNG, JPEG…)
Time needed: 5 minutes
To change the size of an image with the Preview application that comes with any Mac‘s macOS:
- Open the image in Preview.
Here’s how: 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.
Supported file formats: See below for image file types you can resize with Mac Preview.
- Select Tools | Adjust Size… from the menu.
Your own keyboard shortcut: See below for setting up a keyboard shortcut for resizing.
“Adjust Size…” grayed out: If Adjust Size… is grayed out in the menu, export the image to a (lossless) file format which Preview lets you resize such as PNG, resize the copy and export that to the origina format again.
- Check both Scale proportionally and Resample image.
Here’s why: These options ensure the image looks good at the reduced size and, to a limited degree, if you enlarge it, too.
Sample down: Resampling works better when you reduce the image size (discarding—hopefully—insignificant pixels) but may produce artifacts when you scale up; do experiment and examine the results, though.
- Now select pixels under Width: and Height:.
- Enter the maximum width under Width: or the maximum height under Height:.
Watch both: 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 entering100under Width:, Height: has changed to 150. That is too large, so you enter85under Height:. The dimensions are now 57 x 85 pixels.
- Click OK.
- Press Command S to save the image.
Restore the original: 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.
Save with a new name: 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.
Resize an Animated GIF Image on a Mac Using Preview
To change the size of an animated GIF file in Preview on a Mac:
- Open the .gif file in Preview
- Now open Thumbnails in the sidebar.
Here’s how: Select View | Thumbnails from the menu.
Keyboard shortcut: You can also press Command Option 2. - Click the first (topmost) image in the sidebar.
- Holding the Shift key, click the very last (most bottom) image in the sidebar.
Here’s why: Now, all individual frames that make up the animated gif are selected. - Resize the image as above.
File Formats Supported in macOS Preview
| Image File Type | Resize in Preview |
|---|---|
| BMP | Yes You can use Preview to resize Windows BMP files (with the .bmp file extension), though some of the format’s many variants may not work. |
| GIF | Yes You can resize GIF and animated GIF using Preview; see above. |
| HEIF | Yes You can resize images in the HEIF format (using the .heic extension), such as those taken on an iPhone. |
| JPEG | Yes Preview lets you resize images in the JPEG format (with .jpg and .jpeg extensions). |
| JPEG 2000 | Yes Preview lets you resize and save images in the JPEG 200 (JP2) format (with .j2c, .jp2 and .jpf extensions—but not .jpm and .mjp2). |
| Yes You can resize PDF documents using macOS Preview. Do save the PDF as a PNG or other file type before, resize that copy and save it as a PDF file again. | |
| PNG | Yes You can resize PDF documents using macOS Preview. |
| PostScript | Partial Preview lets you open and resize PostScript files, but you can only save them as PDF (or another format supported for saving). |
| PSD | Partial You can change the size and save (or convert) PSD files in Preview (though not all information is retained if you save as PSD). |
| RAW | Partial While you can open and resize many a camera maker’s RAW file format in Preview, you can only save using TIFF or another format supported for saving. |
| SVG | No Preview cannot open, resize or save SVG images. |
| TIFF | Yes Preview can resize and save TIFF scans and images on a Mac (using the .tiff and .tif extensions). |
| WebP | Partial While you can open and resize WebP images in Preview, you can only save them as TIFF files (or another supported saving format) |
| XCF | No Preview does not open or let you resize XCF images (saved with the GIMP image editing program). |
How to Resize an Image with Mac Preview (GIF, PNG, JPEG…): 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 resizing pictures (with “Adjust Size…”) in Preview, say Command Control S.
Will resizing the image change its size (in MB) as well?
Yes, the image will shrink as well, by about the square of the conversion factor.
Example: Resizing to 50% will reduce the file size by about 25%.
Looking for better compression? Find the best (free) online image compression tools revised.
(How to resize an image on a Mac tested with macOS Sonoma 14.2, Ventura 13.1, macOS Monterey 12.0, Big Sur 11.0, and macOS 10.13–10.15; updated February 2024)