Melt guide

Make an image file size smaller on Mac

Four ways to reduce image file size on macOS, from a one-line Terminal command to a drag-and-drop app.

4 min read

You need this image smaller and you don’t want to read 2,000 words about codecs. Fine. Here are four ways that actually work on macOS, from quickest to most powerful.

The two-second way

Right-click the image in Finder → Quick Actions → Convert Image. Pick a format and choose a smaller size (Small, Medium, Large, Actual Size). This uses macOS’s built-in image pipeline and is genuinely fine for one-off shrinking. Limitation: the size presets are pixel dimensions, not file size, so the result is unpredictable.

The Preview way

Open in Preview. File → Export. Pick JPEG, drag the Quality slider, watch the size estimate update at the bottom. Hit Save. This is the most controllable native option — you can see exactly what you’re getting before you commit.

If the image is too big in pixels too, use Tools → Adjust Size first. Set the width to 2000px (or whatever you need) before exporting.

The Terminal way

sips is built into macOS. One line:

sips -s format jpeg -s formatOptions 75 -Z 2000 input.jpg —out output.jpg

What each flag does:

This is the fastest path for one-off jobs once you’ve memorised the command.

The faster way (for more than one)

If you have more than three or four images, the GUI options get tedious and the Terminal command becomes a loop. Download Melt — a $9.99 Mac app built for exactly this.

  1. Download Melt and open it.
  2. Drag images or a folder in.
  3. Pick output format and quality (80 is the default for most things).
  4. Optionally enable Resize.
  5. Click Compress.

The “never makes a file bigger” check means already-optimised images aren’t re-saved larger — they pass through unchanged.

How much smaller will it really get?

JPEGs at quality 80: 40-70% smaller. PNGs through Melt’s quantizer: 60-85% smaller. HEICs converted to JPEG: usually similar size, but compatible with everything. Screenshots saved as PNG converted to JPEG: 80-90% smaller. The biggest wins come from converting format and resizing, not from compression alone — so don’t sleep on the -Z flag.

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