How to Compress an Image on Mac: 5 Free Ways

Your image is too big. An email is bouncing, a website is rejecting the upload, or your portfolio site loads like it’s 2003.

The fastest way to compress an image on a Mac, with nothing installed: open it in Preview, choose File > Export, and drag the Quality slider left. The estimated size updates as you drag. Stop when it’s small enough, save a copy, done.

That solves most cases. If it doesn’t, it’s because you’re pulling only one of the four available levers:

1. Resize, fewer pixels means a smaller file
2. Compress, same pixels but less data per pixel
3. Convert, some formats are simply more efficient
4. Strip metadata, EXIF and color profiles and embedded thumbnails add up

Here’s how to pull each one on a Mac, then how to stack all four in a single pass, plus the format-specific tricks for JPEG and PNG and what changes when the images are going on a website.

1. Resize the image (biggest impact)

The step most people skip, and the easiest win.

A 4000x3000 photo from your iPhone is 12 million pixels. If it’s going on a website where the content area is 800px wide, those extra pixels are pure waste. Resizing to 1600px wide, enough for Retina, cuts the pixel count by 83%.

In Preview: open the image, Tools > Adjust Size, set the width you actually need (1200-1600px for web, 800px for email), keep “Scale proportionally” ticked, then File > Export.

In Terminal, sips is built in and handles a whole folder:

for f in *.jpg; do sips --resampleHeightWidthMax 1600 "$f"; done

--resampleHeightWidthMax caps the longest side, so landscape and portrait both come out sensibly. It edits in place, so copy the folder first.

Typical saving: a 4000x3000 JPEG at 8MB becomes about 1.2MB at 1600x1200. Roughly 85%, from resizing alone.

2. Compress the image

If the dimensions are already right, compression is the next lever.

For photos, 75-85% quality is the sweet spot. Below that, artifacts show up in gradients and skin tones. Above it, you’re storing differences nobody can see on a screen.

In Preview: File > Export, drag the quality slider, watch the estimated size, save when the tradeoff looks right.

In Terminal:

sips -s formatOptions 80 input.jpg --out compressed.jpg

The 80 is quality, on a 0-100 scale. For a folder, writing to a new directory so the originals survive:

mkdir compressed
for f in *.jpg; do sips -s formatOptions 80 "$f" --out "compressed/$f"; done

Typical saving: dropping a JPEG from 100% to 80% quality cuts 40-60% with no visible difference in most photos.

3. Convert to a modern format

The most underused lever, and often the largest after resizing.

If you’re serving images on the web and still using JPEG, moving to WebP cuts a third with no visible quality loss. AVIF goes further with slightly narrower support.

Preview cannot export WebP or AVIF. For those you need a command-line tool (cwebp and avifenc, both via Homebrew) or an app.

4. Strip metadata

Photos carry hidden baggage: GPS coordinates, camera model, lens, exposure settings, color profiles, embedded thumbnails. A single iPhone photo can hold 50-100KB of it.

For one image that’s noise. For 200 images it’s 10-20MB nobody will ever read.

Preview has no one-click strip. In Terminal, with exiftool from Homebrew:

exiftool -all= *.jpg

That strips everything from every JPEG in the folder. It’s destructive, so copy first.

5. Stack them

The real savings come from combining. A worked example on an iPhone photo, 4032x3024 HEIC at 3.8MB:

Order matters a little: resize first, then compress. Compressing a 4000px image and then shrinking it wastes the work.

How to compress a JPEG on Mac

JPEG is lossy every time it’s saved, and that’s the thing to watch. Each re-save degrades the image further, even at the same quality setting. Editing and re-saving the same JPEG five times visibly softens it. Always compress from the original, not from a copy you compressed last week.

sips -s formatOptions above is the built-in route. For lossless gains on top, ImageOptim is a free Mac app: drop files on it and it strips metadata and re-encodes more efficiently, usually 10-20% with zero pixel change.

A JPEG has no transparency. If your image has a transparent background and you convert it to JPEG, that background becomes solid white or black, and there’s no undoing it.

How to compress a PNG on Mac (without losing transparency)

PNG is lossless, so “compressing” it means either encoding smarter or reducing the palette.

pngquant cuts the palette to 256 colors or fewer. Technically lossy, but on screenshots and UI assets the difference is invisible and the savings are large:

brew install pngquant
pngquant --quality=65-80 --output compressed.png input.png

# whole folder, in place
pngquant --quality=65-80 --ext .png --force *.png

Typical saving: 60-80%. A 5MB screenshot becomes about 1MB. Transparency survives.

optipng is fully lossless, for when every pixel must be identical:

brew install optipng
optipng -o5 *.png

-o5 balances speed against compression. -o7 squeezes marginally harder and takes far longer. Typical saving: 10-30%.

Should it be a PNG at all? For a photograph, no. PNG is for flat color, sharp text and transparency. A photo saved as PNG is routinely 4-5 times the JPEG. If you need transparency and small files, WebP does both.

How to compress a photo or picture on Mac

Photo, picture, image: same file, same four levers. The only thing that really changes is where the file lives.

A photo sitting in a folder or on the Desktop. Treat it exactly as above. Preview, File > Export, Quality around 80%, save a copy. A 3.8MB iPhone photo lands under 300KB and you will not see the difference.

A photo inside the Photos app. You cannot compress it in place. Select it, then File > Export > Export Unmodified Original, and compress the exported copy. Photos keeps the original whatever you do to the export.

It is a HEIC. iPhone photos are HEIC by default, and HEIC is already an efficient format. Converting one to JPEG at 80% often makes the file bigger. Resize it instead, that is the lever that actually pays on a HEIC.

To reduce picture size on a Mac in bulk, the sips loop in step 1 takes a whole folder of photos in one pass. If the goal is the Photos library as a whole rather than a few files, that is how to reduce photo library size on Mac.

How to compress images for a website

Three things decide page weight, in this order.

Format. A 1400px hero as JPG might be 800KB. The same image as WebP is around 300KB, as AVIF closer to 200KB. WebP has 97%+ browser support and AVIF is around 93%. For photos on the web there’s very little reason to still be serving JPEG or PNG.

Dimensions. Nobody needs a 4000px image on a webpage. Most content areas are 800-1200px, and even full-bleed heroes rarely need more than 1600px, or 2400px for Retina. Going 4000px to 1600px cuts 75% before compression touches it.

Quality. People agonize over the perfect setting. In practice 80% is visually identical to 100% for photos in a browser. Below 70% you get halos on edges and banding in skies and skin. 75-85% is the range, and 80% is a fine default.

One more thing if you work for clients. Product photos, unreleased designs, screenshots of internal dashboards. Upload those to a web compressor and they land on someone else’s server. Even if the service deletes them afterwards, you still transmitted them, and for healthcare or legal work that’s a compliance problem rather than a preference. Everything on this page except the browser-based services runs locally, and “it never leaves my machine” is a much better answer than “I think they delete them after an hour.”

When the free tools stop being worth it

Everything above is free, and most of it is already on your Mac. For one image, Preview. For a folder at one quality, the sips loop. For PNGs, pngquant. None of that is worth paying to replace.

Where it gets tedious is doing all four levers at once, repeatedly, across a mixed folder. That means Preview for the resize, a Terminal loop for the quality, a separate tool for WebP because Preview cannot export it, and exiftool for the metadata. Four passes, and the settings live in your head.

Picmal does the four in one pass: drop the folder in, set a max width, pick WebP, set quality to 80, tick remove metadata, convert. It reads HEIC and camera RAW too, so a mixed folder goes through together, and it runs entirely on your Mac with no upload and no size cap. It’s $29 once. If you compress a couple of images a month, Preview is genuinely the better answer.

FAQ

How do I compress an image on a Mac?

Open it in Preview, choose File > Export, and drag the Quality slider left. The estimated file size updates as you drag, so you can stop when it is small enough. Preview ships with macOS, so there is nothing to install and nothing to upload.

How small can I make an image without it looking bad?

For photos, 80% JPEG quality is visually indistinguishable from 100% on a screen. WebP and AVIF hold up at 70-75%. For the web aim for under 200KB per image, for email under 500KB.

Does resizing reduce quality?

Resizing down does not degrade quality in any visible way, you are simply using fewer pixels. Resizing up does, because the software has to invent detail that was never captured.

What is the best format for reducing file size?

AVIF gives the smallest files for photos, WebP is close behind with broader support, and JPEG is the safe default that works everywhere. PNG is only smaller for flat color, text, or transparency. For a photograph, PNG is almost always the largest option.

Does re-compressing a JPEG degrade quality?

Yes, every single time. JPEG is lossy on every save, so opening a compressed JPEG, changing it, and saving again softens it further, even at the same quality setting. Always compress from the original, not from a copy you compressed last week.

How do I compress a PNG without losing transparency?

Every method here preserves the alpha channel. pngquant gives the biggest savings by quantizing the palette, typically 60-80%, and keeps transparency intact. optipng is fully lossless and gets 10-30%. Converting to WebP also keeps transparency and usually beats both.

What is the maximum compression I can get on a PNG?

Around 60-80% with pngquant, which cuts the palette to 256 colors or fewer. Fully lossless tools like optipng get 10-30%. If you need more than that, the answer is not PNG at all: convert to WebP, which keeps transparency and usually beats both.

Should I compress images before emailing them?

Yes. Most mail servers reject attachments over 20-25MB, and Gmail stops at 25MB. Resize to 800px wide and export at 80% quality, and a typical iPhone photo drops from 3.8MB to under 300KB. That is small enough to send a dozen at once.

Can I reduce file size without changing the image at all?

Yes. Lossless optimizers like ImageOptim or optipng squeeze out 10-30% by improving how the file is encoded, without altering a single pixel. For bigger reductions you have to resize, re-compress, or change format.

How do I compress a photo on a Mac?

The same way as any image: open it in Preview, choose File > Export, and drag Quality left to around 80%. A 3.8MB iPhone photo drops under 300KB with no visible difference. If the photo lives inside the Photos app you cannot compress it in place, so export it first with File > Export > Export Unmodified Original, then compress the copy.

How do I reduce picture size on a Mac?

Two different things get called size, so pick the one you mean. For a smaller file, compress the picture in Preview at about 80% quality. For smaller dimensions, use Tools > Adjust Size and set the width you actually need. Resizing is the bigger lever of the two, and for a whole folder of pictures the sips loop above handles them in one pass.

Related guides

• Which format should you pick? The best image formats for the web compares JPEG, WebP, AVIF and the rest.
• Moving to a modern format? How to convert images to WebP on Mac walks through it.
• Photos filling your disk? How to reduce photo library size on Mac is about the Photos library specifically: duplicates, screenshots and iCloud offloading.
• Need different dimensions rather than a smaller file? How to resize an image on Mac covers one image or a whole folder.
• Coming from an iPhone? How to convert HEIC to JPG on Mac handles Apple’s format.
• Want the app rather than the walkthrough? Compress images on Mac is the short version.