How to reduce JPEG file size on Mac without losing quality

You’re trying to email a 12 MB photo and your provider is rejecting it, or you’re uploading product photos to Shopify and each one is taking ten seconds. JPEGs that come straight off a modern camera or phone are wildly over-spec for almost any web use — there’s a lot of room to shrink them without anyone noticing.

Two paths

Native macOS. Two reasonable options:

• Preview. Open the image, File → Export, drag the Quality slider toward the middle, save. Preview’s quality slider is roughly accurate — somewhere around 70–80% usually halves the file with no visible loss. Fine for one image at a time.

• Terminal sips. Scriptable and fast:

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

  formatOptions takes 0–100 (or low / normal / high / best). Combine it with a for loop to batch a folder. No GUI, no preview — you set a number and trust it.

Melt. A drag-and-drop Mac app ($9.99 one-time) that re-encodes JPEGs with mozjpeg settings tuned for size-vs-quality, and refuses to write the output if it ends up bigger than the input (a real risk when you re-encode an already-compressed JPEG).

Shrink a JPEG in Melt

1. Open Melt.
2. Drag your JPEG (or a folder of them) in.
3. Leave the format on JPEG and pick a quality — 80 is the standard "looks identical" setting.
4. Click Compress.

The “never makes a file bigger” check matters more than it sounds. JPEGs that have already been compressed once will often inflate when re-encoded; Melt detects that and keeps the smaller original automatically.

Honest tradeoffs

JPEG compression is lossy — every time you re-encode, you throw away a bit of detail. Going from 100% to 80% once is invisible; doing it five times in a row will eventually show. So work from originals when you can, and avoid running the same file through compression repeatedly. For most web, email, and chat uses, quality 75–85 is the boring right answer.