Batch resize images on Mac

You’ve got 200 product photos straight off a DSLR, all at 6000x4000 pixels, and they need to be 2000px wide for the website. Doing them one at a time will take all day. Doing them badly will crash Preview.

Why this happens

Cameras don’t know what you’ll use the photos for, so they save at max resolution. Most cameras default to JPEG quality 95 or higher. Multiply that across hundreds of files and you’ve got a folder you can’t actually use anywhere — too big to upload, too slow to load, too painful to process by hand.

The Preview way

Preview does batch resize, and most people don’t know it. Select the files in Finder, open all of them in Preview at once (they appear in the sidebar). Then:

1. ⌘A to select every thumbnail in the sidebar.
2. Tools → Adjust Size.
3. Set the new dimensions, hit OK.
4. File → Save (or File → Export Selected Images to keep the originals).

This works. It also gets sluggish past about 50-100 images and can outright stall on a folder of 200+ RAW conversions.

The Terminal way

sips is fast and predictable. From the folder containing your images:

mkdir resized && for f in *.jpg; do sips -Z 2000 “$f” —out “resized/$f”; done

-Z 2000 caps the longest edge at 2000px and preserves aspect ratio. To also re-compress at the same time:

for f in *.jpg; do sips -s format jpeg -s formatOptions 80 -Z 2000 “$f” —out “resized/$f”; done

Handles thousands of files comfortably. The downsides are no progress visible until it’s done, no preview, and a typo in the output path is unforgiving.

For ImageMagick users, mogrify is the equivalent:

mogrify -path resized/ -resize 2000x2000 -quality 80 *.jpg

The faster way

Download Melt does batch resize plus compression in one drag.

1. Download Melt and open it.
2. Drag the whole folder in.
3. Enable Resize and set the longest edge to 2000px (or whatever your target is).
4. Optionally set output format and quality.
5. Click Compress. Progress bar shows per-file results.

Mixed-format folders (JPEG, PNG, HEIC) all process in one pass, each format handled correctly. The “never makes a file bigger” check skips images that are already smaller than the target.

How much smaller will it really get?

Resizing 6000px-wide photos to 2000px without changing quality: roughly 11% of the original byte size (linear pixel count is cubed in file size terms — a 3x edge reduction is roughly a 9x byte reduction). Adding quality 80 compression on top: 3-5% of original. A 200-photo folder typically goes from 4-6 GB to 100-200 MB.

For website work, that’s the difference between a usable folder and one that takes ten minutes per page to upload.