You can easily batch resize groups of images within Mac OS X by using the included Preview app, that is, taking a group of pictures set at one or various resolutions, and collectively resize them all together in a group to a new resolution, outputting either as the same file or as a new file saved at the newly desired resolution. Long ago you had to buy expensive third party software for this purpose, but no longer is there a need for any additional downloads or expensive photo editing applications to perform these tasks on a Mac. Instead you only need Preview, which is free with every Mac and every version of Mac OS X!

Here is how to use Previews’ powerful yet easy batch image resize feature to change the resolution of multiple files in one fell swoop, all in a few simple steps.

How to Batch Resize Images in Mac OS X

You will need to launch Preview, which is in the /Applications/ folder, to get started. Preview is also usually the default image editor and can be typically opened by just opening any picture. Once Preview is open, proceed with the following simple directions:

Select all the images you want resized in the Finder, and then open them within the Preview app From Preview, select all of the images that you want to batch resize from the left-side thumbnail drawer (Command+A will select them all) Now, go to the menu labeled “Tools”, and then choose “Adjust Size” Enter a value for what you want the new width and height to be Next, navigate to the ‘File’ menu and click “Save All” or, to save a NEW version that is resized, choose “Export Selected Images…” or “Save As”

If you “Save All”, all the images will instantly save resized over the existing versions. If you “Export” or “Save As”, you’ll create newly resized images in addition to the existing photos.

Choose a path to save the files in the Save dialog to if you’re exporting or using “Save As” features, then just wait for all of the images to finish resizing to their new resolutions. The batch resizing takes place fairly quick, but the precise speed is dependent on your available system resources and speed of the Mac.

This works in Preview that is included in virtually all versions of Mac OS X, learn it once and you’ll have the ability to resize large groups of photos and picture files easily in a batch process that is extremely easy.

The video tutorial below walks through the step-by-step process of using Preview to resize multiple images as opened from the Mac file system, as you’ll see it’s a piece of cake:

Updated: 5/14/2019 for clarification. Note the precise menu language varies slightly per version of Mac OS or Mac OS X, as older versions differ from the most modern incarnations of Mac OS X. Nonetheless, the procedure works in all Preview versions, whether it’s in MacOS Mojave, MacOS High Sierra, Sierra, Snow Leopard, OS X Lion, OS X Mountain Lion, OS X Mavericks, OS X Yosemite, El Capitan, and likely every version where Preview remains as a staple of the operating system.