How to Resize Images on Mac Without Losing Quality

Resizing images on a Mac usually means opening Preview, but the default export options can leave you with a blurry or pixelated photo if you don’t know the right settings. This guide shows you the exact steps to shrink or enlarge an image while keeping it sharp, using only the built-in tools on your Mac. You’ll learn how to use Preview’s resize tool correctly, how to avoid the common quality-killing mistakes, and what to do when the result still looks soft.

What You’ll Need

A Mac running macOS Monterey or later (the steps are similar on older versions).
The image file you want to resize (JPEG, PNG, HEIC, or TIFF all work).
Preview app (comes free with every Mac).
Optional: a destination folder for the resized copy, if you want to keep the original untouched.

Step-by-Step

Make a backup copy (recommended). Before you change anything, duplicate the original file. In Finder, select the image and press Command + D to create a copy. Work on the copy so you can always go back to the original.
Open the image in Preview. Double-click the file, or right-click and choose Open With > Preview.
Open the resize tool. In the menu bar at the top, click Tools > Adjust Size. A dialog box appears with fields for width, height, and resolution.
Choose the right unit. Next to the width and height fields, there’s a drop-down menu. Select Pixels if you’re preparing for web or social media. Select Percent if you want to scale the image by a percentage (e.g., 50% to halve it). For print, use Inches or Centimeters.
Keep the aspect ratio locked. Make sure the checkbox next to Scale proportionally is checked. This prevents the image from being stretched or squished. If it’s unchecked, the width and height change independently, which distorts the picture.
Enter your target size. Type the new width or height. The other dimension updates automatically when the aspect ratio is locked. For example, if you want a width of 1200 pixels, type 1200 in the width field; the height adjusts to keep the same proportions.
Set the resolution (for print only). If you’re resizing for print, you need to know the target DPI (dots per inch). For high-quality print, use 300 DPI. For screen, leave it at 72 or 144—it doesn’t affect digital display. Changing the DPI alone doesn’t change the pixel dimensions; it only changes the physical print size.
Click OK. The image is now resized in the Preview window. You’ll see the new dimensions in the title bar.
Save the resized image. Go to File > Save to overwrite the original (if you’re working on a copy) or File > Export to save as a new file. If you export, choose a format (JPEG for photos, PNG for graphics with transparency) and set the quality slider to Best (or 100%) to avoid compression artifacts.
Check the result. Open the resized file and zoom in to 100% (press Command + 1 in Preview). If it looks sharp, you’re done. If it looks soft, see the Troubleshooting section below.

Common Mistakes

Unchecking “Scale proportionally” – This is the number one cause of distorted images. Always keep it checked unless you intentionally want to stretch the image.
Enlarging a small image too much – If you try to make a 200×200 image into 2000×2000, it will look pixelated. There’s no magic way to add detail that isn’t there. The best you can do is use a small enlargement (e.g., 10–20%) and accept a slight softness.
Saving as JPEG with low quality – When you export as JPEG, the quality slider controls compression. Setting it to 50% will introduce visible artifacts, especially on text or sharp edges. Always use 80% or higher.
Resizing the wrong file – If you resize the original without a backup, you can’t undo it. Always work on a copy.
Ignoring the DPI – For print, a 1000×1000 pixel image at 72 DPI will print at about 14 inches, but at 300 DPI it prints at about 3.3 inches. If you don’t set the DPI correctly, your print will be the wrong size.

Tips

Use the “Export” option instead of “Save” – Export lets you choose the format and quality without overwriting the original. It’s safer and gives you more control.
For web, use 2x resolution – If you’re uploading to a website that displays images at 600px wide, export at 1200px wide. This ensures the image looks sharp on high-resolution (Retina) screens.
Batch resize multiple images – If you have many images to resize, select them all in Finder, right-click, and choose Open With > Preview. Then in Preview, select all thumbnails in the sidebar (press Command + A), go to Tools > Adjust Size, and apply the same settings to all. Then use File > Export Selected Images.
Keep the original format – If you resize a PNG and export as JPEG, you lose transparency and may get a larger file. Stick to the same format unless you have a reason to change.
Use keyboard shortcut – In Preview, you can quickly open the resize dialog with Command + Option + I (that’s the “Get Info” shortcut, but it also opens the Adjust Size window).

Troubleshooting

The image looks blurry or pixelated after resizing.

First, check the zoom level. If you’re viewing at 200% or more, it will look soft. Press Command + 1 to view at actual size.
If it’s still blurry, you likely enlarged the image too much. There’s no way to recover lost detail. Try resizing to a smaller size, or use a dedicated upscaling tool that uses AI (but those are third-party apps, not built-in).
If you’re saving as JPEG, the quality setting might be too low. Re-export with quality set to 100%.

The image dimensions didn’t change as expected.

Check the unit. If you typed 50 thinking pixels, but the unit was set to percent, the image became half its size. Re-open the dialog and confirm the unit.
Make sure you clicked OK and then saved. If you closed the window without saving, the resize was lost.

Preview says the image is too large to open.

This is rare, but if the image is extremely large (e.g., 100 megapixels), Preview may struggle. Try using the Photos app or a third-party editor like GIMP (free) to resize.

I can’t find the “Adjust Size” option.

Make sure you have an image open in Preview. The option is under the Tools menu, not the File menu. If you don’t see it, your Preview version might be outdated; update macOS.

Frequently Asked Questions

Does resizing an image in Preview reduce quality?

If you only shrink the image (make it smaller), the quality remains visually sharp because you’re removing pixels. If you enlarge it, quality decreases because the software has to guess new pixels. Saving as JPEG with a high quality setting also preserves quality.

What is the best format to save a resized image for the web?

For photos, use JPEG with quality 80–90%. For graphics, logos, or images with text, use PNG. For simple images with few colors, you can also use GIF, but PNG is usually better.

Can I resize a batch of images at once in Preview?

Yes. Open all images in Preview (select them in Finder and press Command + O), then select all thumbnails in the sidebar, go to Tools > Adjust Size, apply the settings, and then use File > Export Selected Images.

How do I resize an image to a specific file size (e.g., under 2 MB)?

Preview doesn’t have a direct “file size” target. You can adjust the JPEG quality slider during export to reduce file size. Lower quality = smaller file. Alternatively, reduce the pixel dimensions. Check the file size in Finder after export.

Will resizing affect the EXIF data (like camera info)?

Preview preserves most EXIF data when you save, but some metadata may be stripped if you export to a different format. To keep all metadata, use File > Save rather than Export.

Can I undo a resize in Preview?

Yes, immediately after resizing you can press Command + Z to undo. If you’ve saved and closed the file, you can’t undo unless you have a backup. That’s why working on a copy is recommended.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

More in this bed

The whole Tech How-To bed →