How to Downsize a Photo on Mac | Resize Without Extra Software

Downsizing a photo on a Mac is easiest using the built-in Preview app—open the image, go to Tools > Adjust Size, enter your new dimensions, and save.

Uploading photos that are too large is a common headache—emails bounce, web forms reject the file, and Etsy listings take forever to load. The fastest fix doesn’t cost a thing and lives on every Mac already. Preview, the default image viewer, handles resizing in about ten seconds, no downloads needed. Whether you need to shrink a single photo for a website or batch-resize a folder of screenshots, the tools are built into macOS. Below is the step-by-step method for the most common scenarios, plus what to watch out for so you don’t end up with a distorted or oversized result.

Downsizing One Photo in Preview

Preview gives you exact control over pixel dimensions, resolution, and file size. Here’s the sequence that works on every current version of macOS, including Ventura, Sonoma, and Sequoia.

1. Open the photo in Preview—double-click the file, or right-click and choose Open With > Preview.
2. Click Tools in the menu bar, then select Adjust Size.
3. Check the box labeled Resample image. This ensures the pixel data changes along with the dimensions; leaving it unchecked can actually inflate the file.
4. Enter your target width and height. The pop-up menu beside each field lets you switch between pixels, inches, centimeters, millimeters, and percent. A common web-friendly size is 1920 pixels on the longest side.
5. Lower the Resolution field from the standard 300 ppi (print) to 72 ppi for web use. This alone can cut the file size by more than half.
6. Click OK, then press Command + S or go to File > Save to make the change permanent.

When it works: the file size in the title bar will drop immediately after saving. If the image appears stretched, press Command + Z right away to undo before saving again with the aspect ratio locked.

Batch Resizing Multiple Photos at Once

Resizing one image at a time gets old fast when you have a dozen photos. Preview still handles this—you just need to open files a certain way first.

1. In Finder, select all the images you want to resize (hold Command to pick individual files, or Command + A to grab everything in a folder).
2. Right-click any selected file, choose Open With > Preview.
3. In Preview’s sidebar, press Command + A to highlight every thumbnail.
4. Go to Tools > Adjust Size, enter your dimensions, check Resample image, click OK.

The same window applies the resize to every selected image at once. A quick note: Preview saves the changes to the original files in this workflow. If you want to keep the originals untouched, duplicate the folder first.

Using the Photos App for Library Images

If your photos live inside Apple’s Photos library, the export menu handles resizing during the export step. Open the image in Photos, click File > Export > Export 1 Photo, then pick Small, Medium, or Large from the preset list. For custom dimensions, select Custom and enter your own pixel values. Set JPEG Quality to around 80% for a solid balance between clarity and file size, and switch the color profile to sRGB if the photo is going online—this prevents the washed-out colors that happen when Adobe RGB images hit a web browser.

Setting Up an Automator Quick Action for One-Click Resizing

If you resize photos regularly, a right-click shortcut saves the most time. Open Automator from the Applications folder, click New Document, then choose Quick Action. In the dropdown at the top, set “Workflow receives current” to image files and “in” to Finder. Drag the Scale Images action from the library into the workflow panel, set your preferred size or percentage, then save the workflow with a name like “Resize to 1920px.” From now on, select any image in Finder, right-click, choose Quick Actions > Resize to 1920px, and it’s done.

What Not to Do When Downsizing

Three mistakes cause most of the frustration people run into.

Forgetting to save. Hitting OK in the Adjust Size window only previews the change in Preview—the file on your drive stays full size until you hit File > Save. Missing that step is the number one reason people think Preview didn’t work.

Skipping the aspect ratio lock. The lock icon between the width and height fields keeps your image proportions intact. If you type a width without the lock active, the photo squishes flat or stretches tall. Click the lock to close it before you change any number.

Leaving resolution at 300 ppi for web use. Photos meant for print need high resolution; photos meant for a website or email only need 72 ppi. Dropping from 300 to 72 gives you a much smaller file with no visible quality loss on a screen.

Final Checklist for Downsizing a Photo on Mac

• Open the image in Preview (or select multiple files to batch-resize).
• Go to Tools > Adjust Size and check Resample image.
• Set resolution to 72 ppi for web, 300 ppi for print.
• Enter the target dimensions with the aspect ratio locked.
• Click OK, then press Command + S to save.
• Keep a backup of the original in case you need the full-size version later.