If an image is too large, you can reduce its size in two ways. You can resize and reduce the resolution, or you can export it in a lower quality. Here’s how to resize or reduce photo size on Mac.

You don’t need to use a third-party app to do this on your Mac. It can be done using the versatile, built-in Preview image editing app.

How to Reduce Photo Size by Reducing Resolution

The fastest way to reduce the photo size is by reducing the photo resolution. If a website or an application has an upper limit for a photo file size, first, try reducing the resolution.

Using the Preview app, you can do this for one image at a time or for multiple images at once. First, open the Finder app and locate the image (or images) that you want to resize. Then, simply double-click the file to open it in Preview.

If Preview is not set as the default image viewer, right-click, and choose the Open With > Preview (We recommend that you take some time to set Preview as the default image viewer, as it will make your life easier.).

RELATED: How to Change the Default Application for a File Type in Mac OS X

Now that the photo is open in Preview, it’s time to resize it. Click the Edit button from the top toolbar (It looks like a Pen icon.). Then, from the editing options, click the Resize button (It’s the icon with multiple boxes.).

From the pop-up, first, switch to the “Pixels” option. Then, change the width to around 50% of the original size (You can try out different resolutions.). Instantly, Preview will tell you the new file size of the image. Once you’re happy with the result, click the “OK” button.

Select the Pixels option, and then reduce the Width to resize the image.

Preview will automatically save your changes to the image, but you can use the Command+s option to manually update the image. Now, you can close the Preview window by clicking the red Close button from the top-right corner, or you can use the Command+q keyboard shortcut instead.

When you return to the Finder window, you’ll see the updated file size for the photo.

After the resizing process, the updated photo shows the reduced file size in Finder.

How to Reduce Photo Size by Reducing Quality

What if you can’t resize the image, but you still want to reduce the file size? The Preview app can help you there as well. You can export an image in JPEG format with lower quality (This feature doesn’t support PNG format, but we offer a solution for that in the next section.).

To get started, open the image file in Preview. Then, from the menu bar at the top, click the “File” option and select “Export.”

Go to the "File "section in menu bar and choose the "Export" option.

Once you switch to “JPEG” as the file format, you’ll see a “Quality” slider. Here, slide toward the “Least” quality side, and you’ll see the file size update in real-time.

As Preview is exporting a new image, you can edit the name of the photo as well as the destination from the top. Once you’re happy with the size, click the “Save” button.

In the JPEG format, reduce the quality to reduce the photo size.

Go to the designated folder in Finder and you’ll find the exported image ready to go. In our testing, we were able to reduce a 371 KB PNG photo to a 52 KB JPEG image without having to resize it or experiencing a significant loss in quality.

The exported photo showing the reduced file size in Finder.

How to Compress Photos Using TinyPNG

Don’t want to resize a photo, but still want to use the PNG format? Try TinyPNG.

This website uses intelligent compression to compress the PNG or JPEG file up to 90% without any discernable loss in visual quality. Simply open the TinyPNG website and drag and drop the image files into the upload area.

Drag and drop images that you want to compress in TinyPNG.

Once the compression is done, you can download the photos individually or as a ZIP archive.

Download compressed images from TinyPNG.

As you can see in the screenshot above, TinyPNG managed to compress the 299.7 KB file to just 81.9 KB. That’s a 72% reduction in file size!

Speaking of compressing files, the Preview app doesn’t stop at just photos. You can use the Preview app to compress PDFs as well!

RELATED: How to Compress PDFs and Make Them Smaller

Profile Photo for Khamosh Pathak Khamosh Pathak
Khamosh Pathak is a freelance technology writer who specializes in tutorials. His work has also been published on Lifehacker, iPhoneHacks, Zapier's blog, MakeUseOf, and Guiding Tech. Khamosh has nearly a decade of experience writing how-tos, features and technology guides on the internet.
Read Full Bio »