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Make photos and screenshots smaller on a Mac with Preview, Finder or one command

A 12 MB photo for a web form, or a folder of huge screenshots. Resize and compress images with tools already on your Mac, one at a time or in bulk.

4 min read

A job site wants a photo under 2 MB, or a folder of screenshots has grown to 5 GB. Two things shrink an image: fewer pixels, and stronger compression. Your Mac can do both.

1. Finder: Convert Image

Select one or many images, Control-click, and choose Quick Actions, Convert Image. Pick JPEG or HEIF and an image size such as Medium. New files are saved beside the originals. This is the easiest bulk option.

2. Preview: one at a time, with control

  1. Open the image in Preview.
  2. Tools, Adjust Size: set the width, for example 2000 pixels. Preview shows the resulting size before you save.
  3. File, Export: choose JPEG and move the Quality slider. The file size updates as you move it.

3. Terminal: sips, for batches

sips is built into macOS. Always write to a new folder, because it can overwrite originals:

mkdir -p ~/Desktop/smaller

# Longest side 2000 pixels
sips -Z 2000 ~/Pictures/export/*.jpg --out ~/Desktop/smaller

# Convert PNG screenshots to JPEG at 70 percent quality
for f in ~/Desktop/*.png; do
  sips -s format jpeg -s formatOptions 70 "$f" --out ~/Desktop/smaller/"$(basename "${f%.png}").jpg"
done

What works best

ImageBest approach
Phone photo for email or webResize to 2000 px, JPEG at about 70 to 80 percent
Screenshot of textKeep PNG, or JPEG at high quality to avoid blurry text
Photo to keepLeave the original. HEIC is already efficient
Huge PNG of a photoConvert to JPEG or HEIC, often a tenth of the size

Screenshots add up quietly: see screenshots taking up space. The same idea for documents is in reduce PDF file size.

Common questions

How do I reduce a photo's file size on a Mac?

Open it in Preview, choose Tools, Adjust Size to make it smaller, then File, Export as JPEG with a lower quality. Finder's Quick Actions, Convert Image does the same in bulk.

How do I resize many images at once on a Mac?

Select them in Finder, Control-click, and choose Quick Actions, Convert Image. Or use the sips command in Terminal to write resized copies to a new folder.

Is HEIC smaller than JPEG?

Yes, usually around half the size at similar quality. But not every website accepts HEIC, so JPEG is safer for uploads.

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