How to Resize Images in Bulk on Mac

Resize when an image has more pixels than the place it's going can show. A 4K display is 3840 pixels wide, a blog column far less, and a photo straight from a phone often has more pixels than either.

Resizing removes pixels, which shrinks the file and speeds up uploads and pages. Compression keeps the pixels and stores them more efficiently. For photos going to the web or into an email, doing both gives the smallest files.

Preview resizes several images at once: open them in one window, select all the thumbnails in the sidebar, choose Tools > Adjust Size and enter a new width, height or percentage.

The catch is that Preview resizes the files you opened, so duplicate the folder first. In Terminal, sips -Z 2048 *.jpg scales every JPG in a folder so its longest edge is 2048 pixels, and it overwrites the originals too unless you add --out with a separate folder. Finder's Convert Image Quick Action writes new files, but only offers Small, Medium, Large and Actual Size.

File Acture's Resize Images scales every image in a batch by its longest edge or by a percentage and saves the results as new files.

Set Resize by to Longest edge and type a pixel value, or pick 1024, 1600, 2048 or 3840 px from Presets. Choose Percentage instead to scale everything by the same share, from 5% to 95%. Proportions are always kept, and images already smaller than your setting are never enlarged.

Quality controls the compression of JPEG, HEIC, WebP and AVIF output, and Keep metadata decides whether camera details and location stay; it's off by default. Each image keeps its format, so a HEIC stays HEIC, while GIF, TIFF and BMP files are saved as PNG or JPEG. New files get “-resized” in their names, photos stay upright, and the originals are left as they were.

Pick the smallest size that still looks sharp where the image will be shown.

• 1024 px: thumbnails, chat apps and previews.
• 1600 px: blog posts, newsletters and email.
• 2048 px: large images on websites and shared albums.
• 3840 px: full-screen viewing on a 4K display.
• 50%: halves both edges and leaves a quarter of the pixels, handy when the batch mixes sizes.

For a website, make images about twice as wide as the space they fill on the page, so they stay sharp on Retina screens.

A photo shown 800 pixels wide in a blog column looks best at around 1600 px, and a full-width banner at 2048 px or more. Going further only adds weight, because a visitor's screen can't show pixels the layout never uses. Resize to that width first, then compress to keep each file light.

Resizing sets the pixel size, compressing sets the file size, and converting sets the format, so pick the tool that matches the limit you're facing.

If a form says “under 500 KB”, compress the images to a target size and File Acture reduces the pixel size only if it has to. If a site wants JPG and your photos came from an iPhone, remember that Resize Images keeps HEIC as HEIC, so convert HEIC to JPG as well. When all you know is the width a page displays, resizing is the right first step.

It does unless you turn on Keep metadata, so resized photos don't carry the GPS position they were taken at. To clean photos without resizing them, use Remove Metadata.

Everything runs on your Mac, so the photos are never uploaded. The free version resizes up to 5 images per run, with 3 runs on each Mac; see pricing for Pro.