How to Batch Resize Images on Mac

Steps

1. Download Kompressor for Mac or get it on the Mac App Store
2. Open the Kompressor app
3. Drag and drop your images or folders into Kompressor
4. Select the output format. This can be the format that the images already have.
5. Select what to limit: the width, the height, the long edge or the short edge
6. Select the size: a percentage of the original, or a value in pixels
7. Click on the ▷ (play) button to resize your images offline

Kompressor is free to try: you get 3 conversions, and each conversion can include as many images as you want.

Which resize mode to use

• Max Long Edge is the best choice for a mix of landscape and portrait photos. Each image fits into a square of the size that you set. This is the default.
• Max Width is the best choice for websites, where the layout has a fixed width.
• Max Height and Max Short Edge help with special layouts, for example image rows with the same height.

For the size you can select a percentage (25%, 33%, 50%, 66% or 75%) or enter a value in pixels. Kompressor keeps the aspect ratio, and it never makes an image larger than the original.

Other ways to batch resize images on Mac

Preview

1. Select the images in Finder and open them with Preview. They open in one window.
2. Click a thumbnail in the sidebar and press ⌘A to select all.
3. Choose Tools > Adjust Size, enter the new size and click OK.
4. Choose File > Save.

Be careful: Preview changes your original files. Work on copies.

Finder Quick Action

Select the images in Finder, right-click and choose Quick Actions > Convert Image. Select a format and one of the sizes: Small, Medium, Large or Actual Size. You cannot enter an exact pixel size.

Terminal (sips)

mkdir resized
sips -Z 2000 *.jpg --out resized

-Z 2000 sets the long edge to 2000 pixels and keeps the aspect ratio. Be careful: sips also enlarges images that are smaller than 2000 pixels, and without --out, sips writes over your original files.

When Kompressor is the better tool

Kompressor writes new files. Select a different output folder to keep the originals and the resized images apart. If a file with the same name is already there, Kompressor asks before it replaces the file. It resizes whole folders, and it converts and compresses in the same step. To get the same folder structure in a different output folder, turn on Preserve folder structure in the settings. A resize and a conversion to WebP together often make images for a website ten times smaller. For presets, watermarks and watch folders, see Kompressor vs XnConvert.

Questions

Which size do I need for a website?

Most websites show images at a width of 2000 pixels or less. For a full-width photo, 2000 to 2560 pixels is enough. For a photo in a text column, 1200 to 1600 pixels is enough.

Does a resize reduce the file size?

Yes. Half the width and half the height means a quarter of the pixels, and the file size falls by about the same amount. See also how to compress images on Mac.

Can I make images larger?

No. Kompressor does not upscale images, because that adds no detail.