Stop Mac screenshots being huge PNG files

Drop a Retina PNG screenshot into Slack or Notion and you've just uploaded several megabytes to show a button someone asked about. On a high-resolution display those PNGs are enormous. Switching the default to JPG makes them a fraction of the size — here's the one command, and why Retina is why they're so big.

Why your screenshots are so large

Two things stack up. First, Retina: a Mac display captures at 2× scale, so a region that looks "small" on screen is actually double the pixels in each direction — four times the pixel count of the same area on a non-Retina screen. Second, PNG is lossless: it faithfully stores every one of those pixels with no compression trade-off. High resolution times lossless equals a file that's far bigger than the little screenshot suggests.

Switch the default to JPG

JPG compresses those pixels down to a fraction of the size, with a quality drop you won't notice in a chat message:

# Save screenshots as JPG instead of PNG
defaults write com.apple.screencapture type jpg
killall SystemUIServer

# Undo — back to the default PNG
defaults write com.apple.screencapture type png
killall SystemUIServer

The killall SystemUIServer line applies it right away. From your next capture on, screenshots save as .jpg — a multi-megabyte grab typically drops to a few hundred kilobytes. This is consistent on macOS 13 Ventura, 14 Sonoma, and 15 Sequoia.

Paste instead of upload

For Slack and Notion specifically, you can skip the saved file entirely. Add Control to the screenshot shortcut — Shift+Ctrl+Cmd+4 — and the capture goes to your clipboard. Paste it straight into the message; the app takes the image directly, with no PNG ever written to disk. It's faster, and it leaves no file behind to clean up. Details in how to copy a screenshot to the clipboard on Mac.

Capture just the region

The last lever is how much you grab. A full-screen Retina PNG is the worst case; a tight selection is a small fraction of it. Press Shift+Cmd+4 and drag a box around only the part you're sharing. Combined with the JPG default, a targeted capture keeps even Retina screenshots small enough that no one waits on the upload.

More ways to slim a screenshot

Format is the biggest lever, but not the only one — how to reduce screenshot file size on Mac covers resizing and cropping too.