How to resize an image on Mac without using Preview

You’ve got a 6000-pixel-wide photo and you need it at 1200 pixels for a blog post or a Shopify listing. Resizing in Preview works, but it’s slow when you have ten images to do and the dialog hides behind Tools → Adjust Size like a state secret.

Two paths

Native macOS. Two built-in options:

• Preview. Open the image, Tools → Adjust Size, type a new width (height auto-fills if “Scale proportionally” is on), hit OK, then File → Save. Solid for single images. To batch, you have to select multiple files in Finder, open them all in one Preview window, select all in the sidebar, then Adjust Size — workable but fiddly.

• Terminal sips. Much faster for batches:

  sips -Z 1200 input.jpg --out output.jpg
  

  The -Z flag scales the image so its longest edge is 1200px (preserving aspect ratio). Use -z height width for exact dimensions. Loop it over a folder and you’re done in a second.

Melt. A drag-and-drop app ($9.99 one-time) that resizes and re-compresses in one step. Useful when you want both — say, downscaling a phone photo for the web and shrinking the file at the same time.

Resize images in Melt

1. Open Melt.
2. Drag your image (or folder) in.
3. Enable Resize and enter a max width or longest edge — say 1200px.
4. Pick an output format and quality if you also want to compress.
5. Click Compress.

Melt’s resize keeps the aspect ratio by default and won’t upscale — if your source is already smaller than your target, it leaves the dimensions alone.

Honest tradeoffs

There’s no magic to resizing — every tool uses similar resampling algorithms (Lanczos or bicubic), and the results look nearly identical at the pixel level. The real difference is workflow: Preview is fine for one-offs, sips wins on terminal-friendly scripting, and a drag-and-drop tool wins when you want resize plus format conversion plus compression in a single pass without thinking about it.