2026-10-22
To compress images on a Mac with built-in tools, open the file in Preview and export it at a smaller size. No download, no account, no upload. macOS ships three routes that between them cover nearly every case, and the one people skip is the one that gives you an exact file size.
This matters most when something downstream states a limit: an application form, an email cap, a submission portal. Those care about kilobytes, and only one of the three routes lets you name a number.
Preview is not only a viewer. File, Export opens a panel with a format choice and a quality slider, and the estimated size updates as you move it.
The slider controls quality, not size. If the file refuses to drop far enough, the pixels are the problem, not the slider.
Right clicking a file in Finder gives you Quick Actions, and Resize Image is one of them on recent macOS versions. Pick a width, choose an output folder, and the system writes new files next to the originals.
This is the fastest option for a folder of product shots or screenshots where every file needs the same treatment. It changes dimensions, which is the lever that actually moves size, and it does the whole set at once.
For a folder you will process again next month, macOS ships sips. Create an output folder, then run:
mkdir -p out && sips -Z 1600 *.jpg --out out
The -Z flag caps the longer side at 1600 pixels for every JPEG in the folder and writes the results into out, leaving originals alone. Change 1600 to whatever the destination asks for. It has no quality control, and that is the trade: you get dimensions, not a target file size.
All three routes stop short of the same thing: none of them takes a target in kilobytes. If a form says under 200 KB, you end up guessing with the slider and re-exporting, which is where a browser compressor that accepts the number directly is faster. The 200 KB steps are in /blog/compress-image-to-200kb and the same idea at 100 KB in /blog/compress-jpg-under-100kb.
The other gap is format. Preview exports AVIF and HEIC on newer systems, but support on the receiving end is uneven. For a file someone else has to open, JPEG is still the safe answer, and PNG only when you need transparency, which is explained in /blog/png-vs-jpg-differences.
No. Export writes a new file. The original only changes if you use Save while the image is open in a format that re-encodes, so always export instead.
Because PNG is lossless, so a quality setting has little to work with. Convert the photo to JPEG first, or reduce the pixel dimensions, which is what actually cuts the size. The difference between the two is in /blog/lossy-vs-lossless-compression.
Yes. The Finder quick action handles a batch selection, and sips in Terminal handles a whole folder in one command.
Resizing changes pixel dimensions, compressing changes how efficiently those pixels are stored. Resizing moves file size much further, and the order is covered in /blog/resize-and-compress-image.