Melt guide

JPG vs JPEG on Mac — is there a difference?

Some files are .jpg, others are .jpeg, and macOS seems to treat them differently. Here's what's actually going on.

4 min read

You’ve got a folder where half the photos are .jpg, half are .jpeg, and you’re wondering if you need to do something about it. Spoiler: no, they’re the same file. But the inconsistency can still cause real problems with scripts, batch tools, and certain CMS upload checks.

Why this happens

JPEG is the format (Joint Photographic Experts Group). The original spec was published in 1992, back when Windows file extensions were limited to three characters — so .jpg was forced. Modern systems handle four-character extensions fine, so .jpeg is also valid. Both extensions describe identical files; the bytes inside are identical.

What varies:

The native way to rename

If your tool only accepts .jpg (or only .jpeg), you can rename without re-encoding — they’re the same data.

Finder. Select files, right-click, Rename, pick “Replace Text”, change .jpeg to .jpg. Or use:

for f in *.jpeg; do mv "$f" "${f%.jpeg}.jpg"; done

That’s a rename, not a conversion — no quality loss.

When renaming isn’t enough

If you need to actually re-encode (different quality, smaller dimensions, stripped EXIF), you need a tool that re-saves the JPEG bytes:

sips -s format jpeg -s formatOptions 85 input.jpeg --out output.jpg

Or drag your files into Melt, set the output to JPEG, click Compress. It outputs .jpg regardless of the input extension, plus gives you control over quality and metadata. Download Melt.

Re-export in Melt

  1. Open Melt.
  2. Drag your mixed-extension files in.
  3. Set output format to JPEG.
  4. Pick a quality if you want re-compression.
  5. Click Compress.

What you lose, what you keep

A pure rename (no re-encode) loses nothing — the file is identical. A re-encode through sips or Melt is lossy: you’ll lose a small amount of quality each time. If you’re just standardising extensions, rename. If you’re actually compressing or resizing, re-encode but only once from the original.

So which should you use?

Pick one and stick with it. .jpg is more common on the web and slightly more compatible with old tools. .jpeg is technically more correct. Either works.

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