Mac System Data Too Large? What It Is and How to Shrink It

In System Settings > General > Storage, System Data is often the longest part of the bar, sometimes tens of gigabytes, and there's no Info button to open it. That's because it isn't a folder you can empty; it's an accounting category. To make it smaller, you first need to know what's in it.

#What System Data is

According to Apple, System Data contains files that don't fall into the other categories. It mainly includes files and data used by the system, such as log files, caches, VM files and other runtime resources, as well as temporary files, fonts, app support files and plug-ins. macOS manages this content, you can't manage it from Storage settings, and its size varies with the current state of your Mac. In older versions of macOS, the category was called Other.

In practice, anything macOS can't place under Applications, Documents, Photos, iOS Files or another category ends up here. A lot of it belongs to apps you installed yourself, and you can manage it in the Finder or in those apps.

#What's usually inside

• Caches and temporary files: mostly in ~/Library/Caches and in the per-user temporary folders macOS keeps under /private/var/folders. Browsers, messaging apps, and video and design tools can each hold several gigabytes.
• Logs and diagnostic reports: in ~/Library/Logs and /Library/Logs. Usually small, but they grow quickly when an app keeps crashing.
• App data: ~/Library/Application Support, ~/Library/Containers and ~/Library/Group Containers hold app databases, offline downloads, chat history and attachments. Messaging apps such as WeChat or Slack are often the single biggest item; for WeChat, see WeChat for Mac taking up tens of GB?
• Developer data: Xcode's build caches, simulators and device support files in ~/Library/Developer, plus disk images used by container tools such as Docker. See our guides to Xcode and Docker Desktop.
• Virtual memory files: in /private/var/vm, managed automatically by macOS.
• Local snapshots: Time Machine saves a local snapshot of your startup disk about every hour and keeps it for 24 hours, plus another one before installing a macOS update. Apple says your Mac counts the space used by snapshots as available storage, and deletes snapshots as they age or when space is needed.

Apple puts iPhone and iPad backups and firmware in the iOS Files category, so they aren't counted here.

#Why it suddenly grows

• A macOS update was just downloaded or installed.
• A big video, design or development project filled up caches and build data.
• A messaging app has piled up photos, videos and files.
• Storage settings are still calculating right after you open them, so the number may not be accurate yet. Wait a moment and look again.

#What you can clear and what to leave alone

#Investigate it yourself

#Look inside Library in the Finder

Your personal Library folder is hidden by default. In the Finder, choose Go > Go to Folder (Shift-Command-G), type ~/Library and press Return. Switch to list view, choose View > Show View Options, select "Calculate all sizes", then sort by size to see which subfolder is largest. You can also select a folder and press Command-I to see its size in the Info window.

#Sort folders by size in Terminal

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

This command only reads sizes and changes nothing; the last lines are the largest folders. Once you find one, run the command on it to go a level deeper, for example du -sh ~/Library/Application\ Support/* 2>/dev/null | sort -h | tail -n 15. If Terminal doesn't have Full Disk Access, protected folders are skipped and the totals come out lower than they really are.

#Check local snapshots

tmutil listlocalsnapshots /

You usually don't need to delete snapshots by hand. If you really want them gone, use Apple's method: in System Settings > General > Time Machine, click Options, set Backup Frequency to Manually, wait a few minutes for the local snapshots to be deleted, then switch back to your previous setting.

#Find and clear it with WashBear

Start with Disk Space Analysis to find the biggest contributors. Choose your system disk or your home folder, click Start Analysis, and click down through the largest block in the Treemap or Sunburst. You'll usually see quickly which app inside Library is using the space. It only counts what WashBear can read, so the total may differ from Storage settings.

Then use Deep Cleanup for the parts that can be cleaned. Click Start Scan, and results are grouped into categories such as System caches, User cache files, Application caches, Developer tools, Xcode data and Container caches. The items most closely tied to System Data are:

• Old temporary files and Inactive system cache: only content that hasn't been updated for more than seven days.
• Old diagnostic logs: user-level logs and crash reports older than seven days.
• Additional user caches: app caches that aren't listed separately. Not selected by default, and caches in use are skipped.
• Xcode data: build caches, device support files, simulator runtimes and more. Not selected by default; pick only what you need.
• App leftovers: data left behind by removed apps that can be clearly linked to them.

After the scan, Smart recommendation preselects lower-risk items. Expand any item to see what it is, how cleaning it affects you and where it lives. Cleanup deletes files directly without using the Trash, and the result is recorded in Operation History. Some app data is protected by macOS and can be read only after you turn on access under Settings → Scanning & analysis → Full Disk Access. See Deep Cleanup for details.

#Frequently asked questions

#How big should System Data be?

There's no standard size. The apps you use, any development projects and your habits all affect it. Rather than watching this one number, check whether you have enough available space and whether it keeps shrinking.

#I cleaned up, but System Data didn't get smaller. Why?

First check whether available space went up; the System Data figure often updates slowly. Caches grow back as you use your apps, which is normal. Local snapshots and purgeable caches already count as available space, so removing them won't change available space much. Don't delete unfamiliar system files just to shorten the bar.