How to Resize an Image on Mac (and Bulk Resize a Whole Folder)

To resize one image on a Mac: open it in Preview, choose Tools > Adjust Size, type a width, and save. That is the whole thing, it takes about ten seconds, and Preview is already installed. If that is what you came for, you are done.

Resizing two hundred images is a different problem, and it is the one that actually needs a method. You have 200 product photos at 4000px wide that need to be 1200px for the website. Or 300 conference headshots that need to be 500x500 for the attendee directory. Or a folder of Retina screenshots that need halving for documentation.

Four ways to do that below, three of them free and built into macOS.

Resize a single image on Mac

Preview handles this and nothing else is needed.

1. Double-click the image to open it in Preview.
2. Tools > Adjust Size.
3. Leave Scale proportionally ticked so nothing stretches.
4. Set Width or Height. Switching the unit dropdown to percent is easier when you just want it half the size.
5. Cmd+S to save over it, or File > Export to save a copy and keep the original.

The “Resulting Size” figure at the bottom of that dialog tells you the new file size before you commit, which is handy when you are aiming at an upload limit.

Two things worth knowing. Resample Image should stay ticked when you want fewer pixels. Untick it and you are only changing the DPI metadata, which alters print size and leaves the pixels exactly as they were. And resizing up never really works: the software has to invent detail that was never captured.

For a specific file size rather than a specific width, resizing is only one of the levers: compress an image on Mac covers quality, format and metadata too. For anything involving more than one image, keep reading.

Method 1: Preview, for a batch (free, no install)

Preview handles batch resizing, though the interface is a bit awkward for large batches.

1. Select all the images in Finder
2. Right-click > Open With > Preview
3. In Preview, press Cmd+A to select all images in the sidebar
4. Tools > Adjust Size
5. Enter the width you want (make sure “Scale proportionally” is checked)
6. File > Save All (or File > Export Selected Images for copies)

Watch out: If you use “Save All,” Preview overwrites the originals. If you want to keep the originals, use Export Selected Images to a different folder.

Limitation: Preview applies the exact same pixel size to every image. No “50% of original” or “max 1200px” option, which means a mixed bag of landscape and portrait photos will end up with mismatched effective resizes.

Method 2: Automator Quick Action (free)

Create a right-click menu option that resizes any selected images.

1. Open Automator > New > Quick Action
2. Set “Workflow receives” to image files in Finder
3. Add action: Copy Finder Items (choose a destination folder, which preserves the originals)
4. Add action: Scale Images > set the pixel width or “To Percentage”
5. Save with a name like “Resize to 1200px”

Now select images in Finder > right-click > Quick Actions > “Resize to 1200px.” Done. The resized copies go to your chosen destination.

Best for: A resize you do repeatedly. Once set up, it’s two clicks.

Method 3: Terminal with sips (free)

sips is built into macOS. No installs needed.

Resize all images in a folder to 1200px wide:

for f in *.jpg *.png *.heic; do sips --resampleWidth 1200 "$f"; done

Resize to a maximum of 1200px on the longest side:

for f in *.jpg; do sips --resampleHeightWidthMax 1200 "$f"; done

--resampleHeightWidthMax is the useful one. It resizes the longest side to 1200px regardless of orientation, so landscape and portrait images both come out with sensible dimensions.

Warning: sips modifies files in place. Copy the folder first if you want to keep originals.

Method 4: Picmal (resize and convert in one pass)

Picmal lets you set a max width or height during conversion, so resizing happens alongside any format change. One step instead of two.

1. Drag your images or folders into Picmal
2. Choose your output format (or keep the same format)
3. Set the max width or max height in the resize options
4. Click Convert

Images larger than your specified dimension get resized down. Images already smaller are left alone, they don’t get stretched up. Folder structure is preserved in the output.

Best for: Preparing images for web or email. Resizing and format conversion at the same time (e.g., resize to 1200px + convert to WebP). Processing entire folder hierarchies.

Which method to choose

FAQ

How do I resize an image on a Mac without extra software?

Preview does it. Open the image, choose Tools > Adjust Size, tick Scale proportionally, type a width, then Cmd+S to overwrite or File > Export to keep the original. Preview ships with macOS, so there is nothing to install and nothing to upload.

Does resizing reduce image quality?

Resizing down has no visible quality impact. You’re discarding pixels the display wouldn’t have used anyway, and the resampling algorithm (usually Lanczos) produces clean results. Resizing up always degrades quality because the software is inventing pixels that weren’t there.

What width should I use for web images?

For most websites, the content area is 800-1200px wide. For retina displays, double that: 1600-2400px. A safe default is 1600px wide. It looks sharp on retina screens and is a reasonable file size. Hero images might go to 2400px; thumbnails can be 400-600px.

Can I resize images to exact dimensions (crop to fit)?

Resizing preserves aspect ratio by default, so a 4:3 image stays 4:3. If you need exact dimensions like 500x500, that requires cropping, not just resizing. Preview can crop manually (Tools > Crop), but for batch crop-to-fit, you’ll need a more specialized tool.

How much does resizing reduce file size?

Roughly proportional to the pixel reduction. Halving the width and height (e.g., 4000x3000 > 2000x1500) reduces pixel count by 75%, and file size drops similarly. A 4000px wide JPEG at 8MB typically lands around 1.2MB once it is 1600px wide. To go smaller than that you also have to compress an image on Mac, not just resize it.