Why Mac Screenshots Are So Big, and How to Shrink Them

Two reasons stack up. First, Retina displays render at 2x, so a screenshot of a 1440 x 900 point area is 2880 x 1800 pixels. Second, macOS saves screenshots as PNG, a lossless format. Lossless means every pixel is kept exactly, which is great for text and costly for photos, gradients and video frames on screen.

Screenshots with flat colors and plain text compress well even as PNG. Screenshots that contain a photo, a map, a video frame or a gradient do not. That is why one screenshot is 300 KB and the next is 6 MB.

I built a 2880 x 1800 test PNG: flat interface colors, text-like bars and one noisy photo-like block. It is synthetic, so your own files will differ, but the order of the results holds. I made every other version with sips, cwebp or Smol 1.0.35 at default settings.

Halving the dimensions is the biggest single lever for PNG. Switching to JPG is the biggest lever if you can accept lossy output. Combining both gave the smallest file, and it is also the one with the most visible softening on text.

Open the screenshot in Preview, then:

1. Choose Tools > Adjust Size.
2. Keep Scale proportionally checked and Resample image checked.
3. Set the unit to pixels and halve the width. A 2880 pixel screenshot becomes 1440.
4. Choose File > Export, set Format to JPEG if you want the smallest file, and drag Quality.

Preview shows the estimated file size in the Export dialog for JPEG, so you can stop dragging the slider when the number is small enough. Our Preview file size guide covers its PDF side too.

sips ships with macOS. This halves every PNG on the Desktop that starts with Screenshot and writes a JPG copy:

cd ~/Desktop
for f in Screenshot*.png; do
  sips --resampleWidth 1440 -s format jpeg -s formatOptions 80 "$f" --out "${f%.png}-small.jpg"
done

Use -Z 1440 instead of --resampleWidth to cap the longer side regardless of orientation. The sips command guide lists the rest.

Yes, with a format change. Setting the screenshot type to JPG makes every new capture lossy and far smaller, as the table shows. The two Terminal lines are in how to change the screenshot format on Mac. That is the right call if your screenshots are mostly photos or web pages. For text-heavy ones, keep PNG and shrink only the ones you share.

Screenshots on a scaled display also differ in size. A larger scaled resolution means more pixels and bigger files.

On a Retina screen, a 1x screenshot looks softer when viewed at full size. In an email, a chat or a help article it is usually shown at about 1x anyway, so nobody sees the loss. For a bug report where someone zooms into a menu, keep the 2x version.

Rule of thumb: pick JPG for photo-heavy captures, half-size PNG for interface captures that must stay crisp, and full size only when the detail is the point.

For a screenshot now and then, Preview is enough. For a loop over the Desktop, sips is faster than any app. Neither costs anything.

Smol makes sense when screenshots pile up across folders and you want them all smaller in one drag, from the Finder right-click menu or a watched folder, with nothing uploaded. Watched folders suit fresh screenshots, but they can make already-optimized files larger, so point them at a folder of new captures only. In Smol, the Compress operation keeps the original and writes a copy with a suffix by default. It resizes to fit 2000 x 2000 pixels unless you change it, and that default took my test PNG from 3.9 MB to about 148 KB. It also has no lossless mode. Free ImageOptim is the pick for pixel-identical PNG savings. See the best image compressor for Mac roundup or Smol’s $29 license.