Resize Images on Mac

Resizing Images on a Mac Computer

Reducing the file size of an image is easy to do on a Mac using the Preview app. The Preview app comes pre-installed on all Mac computers and provides a suite of tools for viewing and making basic edits to image files.

Open the Image

To reduce an image's file size in Preview, first open the image file in the Preview app. You can do this by double clicking on the image you want to open. Once the image is open, select 'Tools' from the top menu bar and choose 'Adjust Size' from the drop down menu. This will open the adjust size window.

Adjust the Image

In the adjust size window, make sure the 'Resample image' and 'Scale Proportionately' options are selected near the top. This will allow you to change the resolution of the image, which will reduce its file size. Below the resample option, you'll see a field for entering the new image resolution. The resolution is measured in pixels per inch or dots per inch. The default may be a value of ~72. Enter a lower value to reduce the size of the image. The lower the resolution, the smaller the file size will become. Just keep in mind that making the resolution too low can cause the image to become blurry or pixelated if it's enlarged after resizing.

As you adjust the resolution, Preview will show the new file size for the image at the bottom of the window. You can tweak the resolution until you get the file size small enough for your needs. In order to use the image on FamilyHistoryAi, the image must be 5MB or smaller. Once you have the desired file size, click 'OK' to resample the image with the new resolution.

Saving the Image

The reduced image can be saved. Navigate in the top menu to 'File' > 'Save'. Alternatively, the image can be saved out to a new file. Just go to 'File' > 'Export' to save the resized version of the image. This will create a copy of the file with the edits baked in.


Preview's resize tool makes it quick and easy to reduce image files right on your Mac. With just a few clicks, you can significantly decrease the file size of images to save space or make them faster to transfer and share online. The next time you need to send an image by email or upload it to a website, be sure to run it through Preview first to optimize the file size.