How to Compress an Image on a Mac
Preview, Photos and Mail can all shrink an image on a Mac without installing anything. Apple's steps for each, and what to use when a form wants the file under a set size.
To compress an image on a Mac, open it in Preview, choose File > Export, pick JPEG from the Format menu, lower the quality setting, and click Save. Preview comes with macOS, so there is nothing to install. If a form wants the file under a set size, such as 2MB, Compress Image takes a target in megabytes and runs in your browser, with nothing uploaded.
The Preview, Photos, Mail and Finder steps below follow Apple's own user guides, which listed macOS 27 Golden Gate as the newest version when we read them on 20 October 2026.
Two ways a Mac makes an image file smaller
Every Mac route pulls one of two levers, or both. Lowering the JPEG quality stores each pixel with less detail, and the picture keeps its width and height. Cutting the pixel dimensions leaves fewer pixels to store. For a photo, try quality first. Reach for dimensions when the image is far bigger than the place it's going, such as a full-size camera photo headed for an email.
Which Mac route should you use?
| Where the image is | Use | Lever |
|---|---|---|
| Saved on your Mac, such as a screenshot on the desktop | Preview: File > Export as JPEG | Quality |
| Your Photos library | Photos: File > Export | JPEG Quality and Size |
| An attachment in Mail | Mail's image size menu | Size |
| An upload form with a size limit | Compress Image with a target | Both, automatically |
How to compress an image in Preview
To compress an image in Preview, export a JPEG copy at a lower quality. These steps are from Apple's Preview User Guide page Convert image file types using Preview on Mac:
- Open the image in Preview.
- Choose File > Export.
- Click the Format pop-up menu and choose JPEG.
- Lower the quality. Apple notes that if you choose JPEG, "you can adjust the image's quality." A lower setting gives a smaller file.
- Type a new name or choose a new location, then click Save.
Giving the export a new name keeps your original as it was. For a folder of images, Apple's tip on the same page is to open the files in one Preview window, select them in that window's sidebar, and follow the same steps. If the file is a PNG screenshot, our guide to converting PNG to JPG on a Mac covers what changes when it becomes a JPG.
If quality alone doesn't get the file small enough, cut the pixels too. Apple's page Crop, resize, or rotate an image in Preview on Mac gives the route: choose Tools > Adjust Size, select "Resample image", and enter a lower value in the Resolution field. The full Adjust Size steps, including width and height, are in how to resize an image on a Mac.
How to compress photos from the Photos app
To compress photos from Photos, export them as JPEG with a lower quality or a smaller size. Apple's Photos User Guide page Export photos, videos, slideshows, and memories on Mac gives the steps:
- Select the photos you want.
- Choose File > Export > Export Photos (the menu shows how many you selected).
- Choose JPEG from the Photo Kind pop-up menu. Of the four photo types on Apple's page, it is the one listed for small files.
- Click the down arrow beside Photo Kind to open the JPEG Quality and Size menus, and choose lower settings there.
- Click Export, choose where to save the files, then click Export again.
Photos saves the exported files to the folder you pick, so you can compare their size against the originals before you send them anywhere.
How to send a smaller photo from Mail
Mail can shrink a photo as you attach it. Apple's page Send attachments in Mail on Mac says Mail inserts images at their actual size by default, and that "if different sizes are available" you can pick one from the pop-up menu on the right side of the message header. Picking a smaller size there sends a smaller attachment.
For files over your provider's limit, Apple's answer is Mail Drop, which sends a link instead of shrinking anything. Apple says Mail Drop uploads the attachment to iCloud, where it is encrypted and stored for up to 30 days. If you'd rather the photo stayed on your Mac, compress it before attaching. Our guide to compressing a photo for email covers the attachment limits and how small to aim.
The Finder shortcut: Convert Image
Finder can change an image's format and size without opening it. Apple's page Perform quick actions in the Finder on Mac gives the route: Control-click the file, choose Quick Actions, click More, choose Convert Image, then choose a format and a size. Apple's page doesn't say whether the original is replaced, so check the folder afterwards before deleting anything.
How to compress an image to a set size on a Mac
To compress an image to a set size, use Compress Image in Safari or any other browser and type the limit in megabytes. Preview and Photos make you guess a quality and check the result. The browser tool does the guessing for you.
- Open Compress Image and add one image or up to 50. It takes JPG, PNG and WebP files of up to 50MB each.
- To compress by quality, move the "Compression quality" slider. It runs from 0.3 to 1 and starts at 0.8. The "Estimated output" line shows the size the first file will come out at before you commit.
- To hit a limit instead, type it into "Target max size in MB". The target takes priority over the slider.
- Click Compress and download. One file keeps its name, and a JPG stays a JPG. Several come back together in one zip.
Know what the target does to a stubborn file. For a JPG or WebP, the tool first tries quality settings between 0.4 and 0.92 at full size. If 0.4 still overshoots, it shrinks the width and height, keeping the proportions, and tries again, up to seven more times. A PNG takes a similar route, with fewer colour shades standing in for a lower quality before it shrinks. In our test, two 1600 x 1200 test images given a 0.2MB target came back at 870 x 652 each. If the target can't be reached, you get the smallest file it managed. A file already under the target is handed back unchanged. Compressing an image to an exact size goes through that process in more detail.
A PNG stays a PNG. For PNG files the slider reduces the number of colour shades rather than a JPEG quality, and transparent areas stay transparent. At low settings, smooth gradients such as a sky can show visible bands.
Compress Image doesn't accept HEIC, the format many iPhone photos arrive in on a Mac. HEIC to JPG converts them in the browser and has its own quality slider, from 0.4 to 1, starting at 0.92. Lower it and the conversion compresses as well. On the Mac itself, Preview's JPEG export does the same job, and converting HEIC to JPG on a Mac covers both.
FAQ
Does compressing an image on a Mac lower its quality?
A lower JPEG quality throws away detail, so yes, though at moderate settings it is hard to see on a photo. Each new save at low quality loses a little more, so always compress from the original, not from a copy you already compressed. Lossy vs lossless compression explains the trade.
Why didn't my file get any smaller?
A JPG that was saved at a low quality has little left to give. At a quality setting, Compress Image never hands back a bigger file than you gave it, so if a re-save wouldn't help, you get the original back. Cut the dimensions or set a target instead. Why your image file is so big covers the usual causes.
Can I compress several images at once on a Mac?
Yes. In Preview, open them in one window, select them in the sidebar, and export. In Photos, select several before choosing File > Export. Compress Image takes up to 50 files and returns them in one zip.
Are my photos uploaded anywhere?
Preview, Photos and Finder work on the Mac itself. Compress Image runs inside the browser tab, so the image never leaves your computer. Mail Drop is the exception: Apple says it uploads the attachment to iCloud.