What Is System Data on Mac, and How Do You Reduce It?

You open Storage settings to find out why your Mac is full, and the biggest bar has a name that tells you nothing: System Data. Sometimes it's 20 GB. Sometimes it's 150 GB, and it's bigger than all your photos put together.

This guide explains what's actually in there, which parts are safe to remove, and how to get the space back without breaking anything. Every step works with what's already on your Mac. Where an app helps, I say so, and I say what it doesn't do.

What is System Data on a Mac?

macOS sorts your storage into buckets: Applications, Documents, Photos, Mail, iCloud Drive, macOS itself and a few more. Anything that doesn't fit one of those buckets goes into System Data.

So System Data isn't one thing. It's a leftovers drawer. It holds files your apps make for themselves (caches, logs, saved state), files macOS makes to run (swap, snapshots, indexes), and big things you made that macOS doesn't know how to label (phone backups, virtual machines, developer tools).

On older versions of macOS this bucket was called Other. Apple renamed it System Data in macOS Monterey. Same idea, new name.

Where to see how much System Data you have

On macOS Ventura and later:

Give it a minute. The Storage screen calculates sizes in the background, and System Data is the last number to settle. If you check too early, it can look much bigger than it is.

You'll notice every other row has a small ⓘ button that shows you what's inside. System Data doesn't give you a useful breakdown. That's why it's so confusing, and why the rest of this guide exists.

What's actually inside System Data

Here are the things that usually make up System Data, grouped by whether you can safely remove them. The sizes are rough ranges from ordinary Macs. Yours will be different, but the list of suspects is almost always the same.

Safe to clear

• App caches (~/Library/Caches). Copies of things apps downloaded or worked out before, kept so they open faster. Browsers, Spotify, Slack, Adobe apps and package managers like Homebrew can each hold gigabytes. Apps rebuild what they need.
• Logs and crash reports (~/Library/Logs). Text files apps write while they run. Useful when debugging, safe to remove otherwise.
• Leftovers from apps you deleted. Dragging an app to the Trash doesn't remove its data in ~/Library/Application Support or ~/Library/Containers. For big apps (video editors, games, music software), that can be gigabytes.

Check first

• iPhone and iPad backups. Each one can be the size of the phone's used storage. If you've had several phones, you may have several old backups. Depending on your macOS version, they may show in their own row or be folded into System Data.
• Developer data. Xcode's build folders, old simulators, device support files and Docker's disk image can together reach 50 to 150 GB. Newer macOS versions list some Xcode files under a separate Developer row, but plenty still lands in System Data.
• Virtual machines and big app data. Parallels, UTM and VMware store whole computers as single files. Some apps also keep large libraries inside their containers.

Leave to macOS

• Local Time Machine snapshots. If you use Time Machine, your Mac keeps recent snapshots on its own disk. macOS removes them when it needs the space (more on this below).
• Swap and sleep image (/private/var/vm). When memory runs short, macOS moves some of it to disk. A restart clears it. Never delete these by hand.
• System indexes and temp files. Spotlight's search index and temporary files in /private/var/folders. macOS manages these on its own.

How big should System Data be?

Apple doesn't publish a normal size. From experience, these ranges are a fair guide:

Why System Data keeps growing, and sometimes shrinks on its own

People are often confused when System Data jumps by 30 GB overnight, then drops again a day later. The usual reason is local Time Machine snapshots.

When Time Machine is on, your Mac saves a snapshot about every hour and keeps it for about 24 hours, even when your backup drive isn't plugged in. If you delete a big file, it still lives inside those snapshots, so the space doesn't come back straight away. It moves into System Data instead.

macOS counts this space as purgeable: it deletes the oldest snapshots when an app needs room. So a big System Data number isn't always a problem. It becomes one when apps refuse to install or macOS warns you the disk is full. Step 3 below shows how to remove snapshots yourself.

Caches grow the same way, only slower. Apps add to them every day and rarely clean up after themselves.

Before you delete anything

Three rules keep this safe:

1. Back up first. If you have Time Machine or another backup, let it run before you start.
2. Move to the Trash, don't delete outright. Use Finder's Move to Trash, not rm commands you found online. Empty the Trash only after a day or two of your Mac working normally.
3. If you don't know what it is, leave it. No amount of free space is worth a Mac that won't start.

When you find a big folder and aren't sure, run it through this:

How to reduce System Data on a Mac: 9 steps

The steps go from easiest and safest to more hands-on. Check Storage settings after each one. You may not need them all.

1Restart your Mac

It sounds too simple, but a restart clears swap files and temporary files, and makes Storage settings calculate everything again. It often frees a few gigabytes and gives you an honest starting number.

Choose Apple menu → Restart, wait a few minutes after you log back in, then check Storage again.

2Empty the Trash

Files in the Trash still take up space. Once you're sure you don't need anything in it, Control-click the Trash in the Dock and choose Empty Trash.

While you're there, open Storage settings and look at Recommendations at the top. Turning on Empty Trash Automatically removes anything that's been in the Trash for 30 days.

3Remove local Time Machine snapshots

If you use Time Machine, this is often the single biggest win. Open Terminal (in Applications → Utilities) and paste this to see your snapshots:

$ tmutil listlocalsnapshots /

To delete one, copy the date part of its name and use it in this command. You'll be asked for your Mac password, and nothing shows while you type it. That's normal.

$ sudo tmutil deletelocalsnapshots 2026-09-29-101530

4Clear app caches

App caches are the most common cause of a bloated System Data, and the safest to clear. Here's how to do it by hand:

1. In Finder, choose Go → Go to Folder (⇧ ⌘ G) and type ~/Library/Caches.
2. Switch to list view (⌘ 2), then choose View → Show View Options and tick Calculate all sizes. Click the Size column to put the biggest folders at the top.
3. Quit the app a big folder belongs to (the names usually give it away, like com.spotify.client). Then move that folder to the Trash.
4. Restart your Mac. The apps build fresh, much smaller caches when you next open them.

5Delete old iPhone and iPad backups

If you've ever backed up a phone or tablet to your Mac, check this. Each backup can be tens of gigabytes, and old ones for phones you no longer own are pure waste.

1. Connect your iPhone or iPad (or skip this if you just want to see the list).
2. Open Finder and click your device in the sidebar. On the General tab, click Manage Backups.
3. Select a backup you don't need, click Delete Backup and confirm.

Backups are stored in ~/Library/Application Support/MobileSync/Backup, which is also a handy way to see how much space they use.

6Clear developer data (if you write code)

If you've ever installed Xcode or Docker, this step can free more than all the others together. Everything here gets rebuilt or downloaded again when you need it.

• Xcode build files: move ~/Library/Developer/Xcode/DerivedData to the Trash. Xcode rebuilds it on your next build.
• Old device support files: in ~/Library/Developer/Xcode/iOS DeviceSupport, remove folders for iOS versions you no longer test on.
• Simulators: remove simulators for runtimes you've already uninstalled, and old runtimes in Xcode → Settings → Components (called Platforms in some versions).

$ xcrun simctl delete unavailable

• Docker: its whole disk lives in one file that only grows. Removing images, containers and build cache you're not using shrinks what's inside it:

$ docker system prune

• node_modules and package caches: old projects often each have a node_modules folder of several hundred megabytes. Delete them in projects you're not working on; running npm install brings them back.

7Remove leftovers from apps you've deleted

When you drag an app to the Trash, its data stays behind. Go to these folders (with Go to Folder as in step 4) and look for names of apps you no longer have:

• ~/Library/Application Support
• ~/Library/Containers and ~/Library/Group Containers
• ~/Library/Preferences (tiny files, but tidy)

Only move a folder to the Trash if you're sure its app is gone. Some folder names don't match the app name exactly, and some belong to apps you still use. When in doubt, leave it.

8Find anything else that's big

If System Data is still large, something specific is hiding. This Terminal command lists the 15 biggest folders in your Library, biggest last:

$ du -sh ~/Library/* 2>/dev/null | sort -h | tail -n 15

Things that often turn up here:

• Virtual machines from Parallels, UTM or VMware. If you no longer use one, delete it from inside the app so it cleans up properly.
• Mail downloads and attachments, or a Messages history full of videos. Usually these show in their own rows, but not always.
• Music and video app libraries, like GarageBand and Logic sound packs, or Final Cut Pro render files.

9Turn on Apple's storage helpers and keep macOS updated

Back in Storage settings, the Recommendations section offers a few switches that stop things piling up again:

• Store in iCloud keeps older files and photos in iCloud and downloads them when you open them.
• Optimize Storage removes movies and TV shows you've already watched in the Apple TV app.
• Empty Trash Automatically, mentioned in step 2.

Also install macOS updates when they come. Once in a while, a system process gets stuck writing huge log files, and an update is what fixes it.

What not to do

Plenty of advice online will free space and cause new problems. Skip these:

• Don't delete anything in /System, /private/var or /usr. Most of it is protected anyway, and the rest is there for a reason.
• Don't empty your whole ~/Library folder. It holds your settings, passwords, mail and app data, not just caches.
• Don't paste sudo rm -rf commands from forums unless you understand every part. They delete instantly, without the Trash.
• Don't turn off Time Machine just to get rid of snapshots. Remove the snapshots and keep the backups.
• Don't reinstall macOS as a first move. It's hours of work for something the steps above usually fix in half an hour.
• Be wary of cleaner apps that delete without showing you what. A good tool lists every file, lets you choose, and moves things to the Trash so you can change your mind.

The faster way: see everything in one window

Everything above works, but it means visiting a dozen folders, calculating sizes in Finder and remembering which folder belongs to which app. That's why I built DiskMate. It's one option, and here's honestly what it does.

• Steps 4, 6 and 7 in one list. DiskMate's Cleanup page finds app caches, logs, Xcode build files, device support and simulator caches, node_modules folders and package caches, and adds them up. You tick what goes.
• App leftovers, found for you. The Apps page shows each app's real size including its files in ~/Library, and removes the app and its leftovers together.
• Step 8 without Terminal. The Space page ranks every folder by size, including the hidden ones in Library, as a list or a treemap you can click into.
• Nothing disappears by surprise. Everything goes to the Trash first, so you can put it back. The app never sends anything off your Mac.

What it doesn't do: DiskMate leaves local Time Machine snapshots and swap files to macOS, so steps 1 and 3 are still worth doing by hand. It runs on Apple silicon Macs with macOS 14 Sonoma or later.

Quick checklist

Bookmark this for next time the “disk almost full” warning shows up:

Frequently asked questions