How to resize an image on Mac, crop it and compress it

How to resize an image on Mac: the short answer

Start with what you need to change. For exact pixels, use Preview’s Adjust Size. For one part of the picture, crop it in Preview or Photos. For a smaller file in MB, use Export and its Quality slider. Three questions lead you to the right tool:

Apple’s guides give the same Preview and Photos steps for macOS Tahoe 26 and macOS 27. Only Finder’s Convert Image gains a step in macOS 27. Here are the main built-in routes and what each changes:

How to crop an image on a Mac in Preview

Select the part you want to keep, then click Crop, and Preview discards the rest. These are the steps from Apple’s Preview guide:

1. 1

   Show the Markup toolbar

   Open the image in Preview. If the Markup toolbar is hidden, click the Show Markup Toolbar button.

2. 2

   Click Rectangular Selection, then drag

   Drag over the part you want to keep. For an exact size, choose Tools, then Show Inspector, open the Crop Inspector and choose a unit.

3. 3

   Click Crop

   Click the Crop button in the Markup toolbar. On macOS 26.5.1, Preview’s own menu also lists Tools, Crop with Command-K, though Apple’s shortcut page leaves it out.

Preview saves the crop into the file you opened. In Apple’s words, “Preview automatically saves changes for you as you work.” To keep the original, choose File, Duplicate first and crop the copy.

How much does a crop save? We cut the middle square from our 4964 × 2782 photo with sips, the command-line image tool built into macOS. The 2782 × 2782 square came to 964.8 KB, against 9,804.3 KB for the whole photo. The square keeps 56% of the pixels but only 10% of the bytes. That is because sips also saves a new JPEG at its own default quality.

Crop images on Mac in Photos

Photos keeps the original, “so that you can always undo your changes”, in Apple’s words. The steps, from Apple’s Photos guide:

1. 1

   Double-click the photo, then click Edit

   Or select its thumbnail and press Return.

2. 2

   Click Crop, or press C

   Apple’s shortcut list for Photos gives C for a crop.

3. 3

   Pick a shape, or drag the frame

   The sidebar holds the aspect ratios. Apple names Square, 4:5, 16:9 for high-definition video, and Custom.

4. 4

   Click Done

   To go back at any time, choose Image, then Revert to Original.

A crop “changes its appearance everywhere in Photos”, Apple warns. To keep both versions, choose Image, Duplicate 1 Photo (Command-D) and crop the duplicate. On macOS 27, Photos adds Extend and Reframe under Tools. Apple offers both “With Apple Intelligence”, which its page, read on 4 October 2026, says is not available in all languages or regions.

The library’s original never gets smaller, so a smaller file is an exported copy. Apple’s Photos export steps say “Choose File > Export > Export [number] Photos.” Then set the Photo Kind, the JPEG Quality and the Size. Apple names no sizes in pixels.

Resize an image on Mac: Preview’s Adjust Size

Adjust Size sets an exact width and height in pixels, and Apple’s steps for a smaller file start there too. In Preview:

1. 1

   Choose Tools, then Adjust Size

   For several images, open them in one window and select them in the sidebar first.

2. 2

   Keep Scale proportionally ticked

   Change the width and the height follows, so the picture keeps its shape.

3. 3

   Choose pixels or percent, then type the width

   The unit menu sits next to Width and Height. Or choose a size from Fit into. One side may then come out smaller than the size you chose, to keep the proportions.

4. 4

   Tick Resample image, then click OK

   “The new size is shown at the bottom,” Apple says, so you see it before you click.

Like a crop, Adjust Size changes the file you opened, so duplicate it first to keep the original.

Unticked, Resample image makes the dimensions smaller “without losing any detail”, Apple says. To reduce the file size, Apple’s steps tick it, then enter a smaller value in the Resolution field.

How to compress an image on Mac: Export and the Quality slider

Export saves a new copy at the format and quality you choose. The file you opened stays as it was. The steps from Apple’s Preview export page:

1. 1

   Choose File, then Export

   For several images, open them in one window and select them in the sidebar first.

2. 2

   Pick a format

   Apple lists HEIC, JPEG, JPEG-2000, OpenEXR, PDF, PNG and TIFF. Hold Option as you click the Format menu for older formats. WebP and AVIF are not in Apple’s list.

3. 3

   Lower the Quality slider

   “If you choose JPEG or JPEG-2000, you can adjust the image’s quality,” Apple says. A lower quality makes a smaller file.

4. 4

   Name the copy, then click Save

   Choose another folder if you want the copy somewhere else.

What a lower quality did to our photo

Apple gives no file sizes for the slider’s positions. So we used sips, which takes the quality as a percent, on the same 9.8 MB photo. Every pixel stayed; only the quality changed.

At sips quality 60, quality alone cut the file by 86%. The photo kept every pixel and fell from 9.8 MB to 1,390.7 KB. As a sips HEIC, it came to 852.2 KB. Apple’s quality sentence names JPEG and JPEG-2000 only, so it does not say whether HEIC gets the slider.

Convert from the Finder: Convert Image

Convert Image changes an image’s format or size from the Finder, without opening an app. Apple’s Finder guide gives these steps:

1. 1

   Select the image in the Finder

   Apple’s steps start from one selected file, on the desktop or in a Finder window.

2. 2

   Control-click it, then choose Quick Actions

   The same actions sit as buttons at the bottom of the Finder’s Preview pane.

3. 3

   Choose Convert Image, then a format and a size

   On macOS 27, click More first. Apple’s example turns an iPhone .heic photo into a .jpeg or .png.

Apple first documents Convert Image for macOS 12 Monterey. Apple does not state the sizes in pixels or the formats beyond that example. Nor does it say how many files one run takes, or where the new file goes. We did not measure Convert Image either, so no sizes for it appear here.

For many images at once, two routes have documented steps. In Preview, select every image in the sidebar, then use Adjust Size or Export as for one. In Terminal, sips resizes a whole folder in one line.

Resize from Terminal with sips

The sips command is built into macOS and runs in Terminal. Its name stands for “scriptable image processing system”. Apple’s support site has no page for it, so its manual, man sips, is the guide. These two lines resize and compress a copy:

• -Z 1600 fits the longer side to 1600 pixels, for portrait and landscape photos alike.
• -c 2782 2782 crops to a height, then a width. With no offset, our square came from the middle.
• -g pixelWidth -g pixelHeight prints the size, so you can check the result.
• sips --formats on macOS 26.5.1 lists AVIF and HEIC as formats it writes, and WebP as one it only reads.

Many files at once with sips

Give sips several files and a folder after --out. The folder must exist first; sips stopped with an error when it did not.

We ran it on 2 copies of our photo. Each came out 1600 × 896 at 216.0 KB in the new folder, and both originals stayed as they were.

How much smaller each size makes the file, measured

Fewer pixels make a smaller file, and the encoder decides how much smaller. We resized our 9.8 MB, 4964 × 2782 photo to 5 widths with sips on macOS 26.5.1. Here is the photo at each width, drawn to one scale:

Through our engine at Auto, the same widths came out about half the size of the sips files:

At 1600 wide, sips saved 216.0 KB and Blinkimg 104.9 KB, 51% smaller. Across the 5 widths, the engine’s file was 50% to 57% smaller. At some widths the heights differ by a pixel. In our runs, sips rounded the height down and the engine to the nearest pixel.

Is the gap the resize or the encoder?

The encoder. To test it, we resized the photo to 1600 wide once and kept those pixels lossless. Then we gave the same pixels to both tools. At its default quality, sips saved 239.7 KB; Blinkimg at Auto saved 104.9 KB.

PSNR measures how close the pixels stay to the source, and higher is closer. The sips file keeps more detail: 40.6 dB against our engine’s 38.2 dB. The sips file pays for that with 2.3 times the bytes. Here the sips file weighs 239.7 KB, not the 216.0 KB in the bars. The reason: sips encoded pixels we resized, not pixels it resized itself.

Reduce image file size on Mac without an app

Apple documents no Mac tool that takes a target size, such as under 1 MB. In a browser, the reduce image size in MB tool lands at or under the number you type. The image compressor saves at Auto, and resize image sets exact pixels.

For iPhone photos in HEIC, HEIC to JPG converts them for sites that ask for JPEG. For the phone itself, read the guide on how to resize an image on iPhone. That guide covers Preview on iOS 26 and later.