How to Compress an Image on a Mac (Preview, Finder, Photos)

By NexGama Studio · Updated October 28, 2026 · 2 min read

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Macs can shrink images without installing anything. The right method depends on whether you have one picture, many pictures, or a strict size limit like “under 100 KB”.

Method 1: Preview (one image, with a quality slider)

Open the image in Preview (double-click it in most cases).
Optional: make it smaller first with Tools → Adjust Size. Enter a new width, such as 1600 pixels, with “Scale proportionally” ticked.
Choose File → Export.
Set Format to JPEG and drag the Quality slider to the left. Preview shows the estimated file size under the slider.
Click Save. Use a new name if you want to keep the original.

Lowering the width has a much bigger effect than the quality slider alone. Halving the width makes the file roughly four times smaller.

Method 2: Finder Quick Action (many images at once)

Select one or more images in Finder.
Right-click (or Control-click) and choose Quick Actions → Convert Image.
Choose JPEG as the format and Small, Medium or Large as the image size.
Click Convert. New, smaller copies appear next to the originals.

Convert Image is available on recent versions of macOS (Monterey and later). It is also a quick way to turn iPhone HEIC photos into JPG.

Method 3: Photos app

Select the photos in the Photos app.
Choose File → Export → Export Photos.
Set Photo Kind to JPEG, lower the JPEG Quality to Medium, and set Size to Small or Medium.
Click Export and choose a folder.

Need an exact size, like under 100 KB or 50 KB?

The built-in tools make you guess. Online forms and job portals often reject a photo that is even 1 KB over the limit. Use the Image Compressor instead: type the target size (for example 100) and it finds the highest quality that fits. It runs in Safari or Chrome on your Mac, and the photo is never uploaded.

If the form also wants exact dimensions, set them first with the Image Resizer. Our guide to compressing an image to 100 KB covers the common limits.

Quick tips

Photos → JPG, screenshots → PNG. Saving a photo as PNG makes it bigger, not smaller.
Mac screenshots are PNG by default and often 2–5 MB. Convert them to JPG if they don’t contain small text.
iPhone photos arrive as HEIC. Many websites reject them; convert with HEIC to JPG or the Convert Image quick action.
Keep the original. Compressing removes detail permanently, so save the smaller copy under a new name.

Tools used in this guide

Image CompressorShrink JPG, PNG or WebP files, optionally to a target size in KB. Image ResizerSet exact width and height in pixels, with aspect lock. HEIC to JPGTurn iPhone HEIC photos into JPGs that open anywhere.