What is System Data on Mac, and how to shrink it

What System Data is

Open System Settings › General › Storage and macOS splits your disk into categories: Applications, Documents, Photos, Mail, iCloud Drive, macOS and so on. Apple describes System Data as the space used by Apple's and other developers' files that don't fit any of those. Older versions of macOS called it Other.

It isn't one folder, so there is nothing called "System Data" to open or delete. It's the sum of many places, worked out as what's left once the other categories are counted. That is also why it changes size from one hour to the next, and why the number can look wrong just after a large update or a big download.

What's usually in it

Step 1: restart, then look again

A restart empties the swap files macOS uses as extra memory, clears temporary files, and lets it finish removing snapshots and update files it was waiting to delete. It's the quickest fix, and it often takes gigabytes off System Data. Give Storage settings a minute to recalculate before you read the new number.

Step 2: delete old Time Machine local snapshots

When Time Machine is on, macOS keeps snapshots of your disk on the disk itself, so you can restore files even when the backup drive isn't connected. They count as System Data. macOS removes them on its own when it runs short of space, and deletes each after about a day, but you can remove them now:

1. Open Terminal and list them: tmutil listlocalsnapshots /
2. Each line ends in a date like 2026-10-27-101530. Delete one with tmutil deletelocalsnapshots 2026-10-27-101530, using the date from your list.

Your backups on the Time Machine drive are not affected; you only lose the local copies.

Step 3: clear app caches and old logs

1. Quit the apps whose caches you want to clear.
2. In Finder, choose Go › Go to Folder (⇧ ⌘ G) and type ~/Library/Caches.
3. Choose View › as List, then View › Show View Options and tick Calculate all sizes, and sort by Size.
4. Move the biggest folders of apps you've quit to the Trash. Delete what's inside Caches, never the Caches folder itself.
5. Do the same in ~/Library/Logs, then empty the Trash.

Caches come back as you use your apps; that's what they are for. Clearing them helps most when one app's cache has grown out of proportion, such as a browser, Spotify or Xcode's DerivedData. Junk Cleaner finds the usual suspects for you.

Step 4: find the big app data

If System Data is still large, it's usually one app storing a lot: Docker's disk image, a virtual machine, an old iPhone backup, or years of Messages and Mail attachments. To find it, open Terminal and run:

du -sh ~/Library/* ~/Library/Containers/* ~/Library/Application\ Support/* 2>/dev/null | sort -h | tail -20

The last lines are the largest folders. Free their space from inside the app that made them, not by deleting the folder:

• Docker Desktop: remove unused images and volumes, or lower the disk image size in its settings.
• Virtual machines (Parallels, VMware Fusion, UTM): delete VMs you no longer use from the app's own list.
• iPhone and iPad backups: select the device in Finder's sidebar, click Manage Backups, and delete the old ones.
• Xcode: delete old simulators with xcrun simctl delete unavailable, and old device support files from ~/Library/Developer/Xcode/iOS DeviceSupport.

What not to do

• Don't delete anything in /System, /private/var or /Library/Apple by hand. macOS manages them, and some of it is needed to start up.
• Don't turn off System Integrity Protection or virtual memory to save space. You gain little and lose a lot of safety and stability.
• Don't run a "clear all caches" command you found online with sudo. Clear caches app by app instead.

What purgeable space means

Select your disk in Finder and choose File › Get Info, and you may see more space Available than Storage settings shows as free. The difference is purgeable: local snapshots, iCloud files that are also stored online, and caches that macOS deletes by itself the moment it needs the room. You don't have to clear it before installing something large.

See and shrink System Data with Tidy My Mac

The steps above work, but they mean Terminal commands and a lot of folder sizes. Tidy My Mac shows the same things in one window:

• Disk Map draws a treemap of your home folder or the whole disk, so the folders behind System Data show up as the biggest blocks, ready to open or move to the Trash.
• Junk Cleaner finds caches, logs, old installers and iOS backups, and developer junk from Xcode, Docker and Homebrew, with the risky ones left unticked.
• Large Files lists disk images, virtual machines and archives by size, each labelled Safe to delete, Review or Keep.
• Ask answers "why is my disk full?" in plain words, from what the app measured on your Mac.

Nothing is removed before you see it, and most of it goes to the Trash. To remove whole apps and their leftovers, see how to uninstall apps on Mac completely.