Make smaller Mac screenshots for email and the web

A PNG screenshot that's fine on disk becomes a nuisance the moment you attach it to an email or drop it into a web form with a size cap. Saving screenshots as JPG cuts the file size dramatically before you ever hit send. Here's the switch, plus ways to trim size further when a limit is tight.

Switch screenshots to JPG

The single biggest win is changing the default format. PNG stores every pixel losslessly, which makes screenshots heavy; JPG compresses them to a fraction of the size with a quality drop you won't see in an email:

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

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

A full-screen grab that was 3–4 MB as a PNG typically lands under half a megabyte as a JPG — often small enough to clear an attachment limit or upload cap on the first try. This works the same across macOS 13 Ventura, 14 Sonoma, and 15 Sequoia.

Capture less to send less

The other half of file size is how much you capture. A screenshot of a single button is far lighter than the whole screen around it:

• Press Shift+Cmd+4 and drag a box around just the part that matters.
• Or press Shift+Cmd+4 then Space to grab a single window rather than the full desktop.

Cropping tight before you capture beats shrinking a huge image afterward, and it keeps the recipient focused on the thing you're pointing at.

When JPG still isn't small enough

If a form has a hard cap and your JPG still won't fit, resize the image down — a screenshot from a Retina display is often twice the pixel dimensions anyone needs on the web:

1. Open the screenshot in Preview.
2. Choose Tools → Adjust Size and reduce the width — halving it roughly quarters the file.
3. Export with File → Export and lower the JPEG quality slider if you need to go smaller still.

Between JPG format, a tighter capture, and a resize, almost any screenshot can be brought under an email or upload limit. For a fuller rundown of the options, see how to reduce screenshot file size on Mac.

Resize in a couple of clicks

Need the pixel dimensions down, not just the format? How to resize an image on Mac covers the fastest ways to scale a screenshot before you send it.