Why System Data takes so much space on your Mac
If you’re a Mac user running low on space, one of the first things you’ll probably check is your storage.
It’s common to find Mac System Data large and it can be frustrating when you don’t know what’s causing it. So, what exactly is System Data, why does it take up so much space, and how can you reclaim some of it?
In short, System Data is huge because of the accumulation of local Time Machine snapshots, log files, caches, and files left over after an incomplete app removal. A certain amount of it is normal, but not too large. Below, we’ll break down what’s included in System Data, so you know what you're looking at before deleting any files.
In this article, we'll also explain what System Data is, why exactly it grows large, and help you understand how much of it is normal. We'll also cover every safe clearing method so that when you're ready to clean it up, all you have to do is just follow our step-by-step guide on clearing System Data.
What is System Data on Mac
System Data on Mac includes everything that doesn’t fit into the usual storage categories — like Applications, Music, Documents, Photos, Mail, and so on. If a file doesn’t clearly belong to one of those, macOS puts it into System Data.
This includes things like:
- System logs and temporary files
- Caches
- Virtual memory files
- Fonts
- App support files and plug-ins
- Old backups (including iTunes backups if they weren't deleted and iOS files)
- Browser data (including Safari reading list and bookmarks)
- Game data
While macOS manages most of it automatically, System Data can grow large over time as those unneeded files pile up.
Tip: Local snapshots are temporary Time Machine backups stored on your Mac for 24 hours. If you've been moving a lot of files around, this category may quickly inflate. They usually clear on their own within a day — Time Machine is designed to remove them when space is needed or as they age.
How to check System Data on Mac
The steps to check System Data on your Mac depend on which version of macOS you're using.
Here's how to do it on macOS Ventura and later:
- Open System Settings > General > Storage.
- Either wait for the colored graph to load and hover the mouse pointer over the dark gray color or scroll down until you see System Data.
If you have macOS Monterey or older, follow these steps:
- Go to the main Apple menu (Apple icon on top left) and choose About This Mac.
- Click Storage and wait for the graph to load.
- Hover the mouse pointer over the dark gray color. You can also click Manage and go to System Data (Other) in the sidebar of the open window.
How much System Data is normal on Mac?
The default size of the macOS system is 12 GB. This implies that having around 12GB of System Data is normal. Your operating system should automatically maintain and clear this category, but this doesn't always happen, resulting in a loss of precious disk space and often being the reason why "System Data" takes up so much storage.
However, if your "System Data" shows something around 14-20 GB, you have pretty good chances to slim it down to that original size. This is good news, but you'll have to delete some unimportant files.
What makes System Data so large
Each category below can grow beyond its useful size. Keep on reading to see what each of them is and why they build up and follow our guide on clearing System Data storage on Mac for click-by-click removal instructions.
Apple's built-in Optimize Storage tool won't show you what's inside
One problem is that it's also tricky to manually identify all items categorized in "System Data" because when you go to Apple's Built-in Storage optimizing tool, you can't click "System Data" to investigate further.
But have you noticed? Apple suggests that you clean up only those files and documents that are created by you. This doesn't address the macOS System Data large problem, but the categories below explain where that space goes.
Temporary files that a restart cleans
Over time, your Mac collects temporary files, caches, and other unnecessary data that can take up valuable storage space. A quick restart helps clear out these files, reset your apps, and stop any unresponsive background processes. And it also frees up memory.
Cache files
Browsers, apps, and macOS create files to speed up repeated tasks — these are cache files. They accumulate over time. They live in the System and user folders. You might notice that there are files related to the apps you've removed months ago.
Be very careful when moving or deleting files in the Library folder. If you’re not sure what something does, it’s best to leave it alone — removing the wrong files can cause apps to break or even prevent your Mac from starting up.
Log files
Log files are records of what macOS and apps are doing. They, too, create these files by themselves. Old log files serve no everyday purpose, but they are not deleted automatically, and so may stay in the Library folders and make System Data grow large.
Local Time Machine snapshots
macOS stores local copies of your Time Machine backups. Time Machine should normally delete them as they age or when space is needed. However, it also keeps a snapshot of the last successful update, and so it may expand this category.
If snapshots are taking more space than they should, both the manual cleanup route (using Disk Utility or Terminal) and CleanMyMac's Thin Time Machine Snapshots tool in its Performance feature are covered in detail in our clearing guide.
Tip: Don't delete your local copies if you think you might need them in the future.
Application leftovers
Applications often store logs, caches, and other data on your Mac, and sometimes these files stick around even after you've deleted the app. These leftovers are also in the Library folders. 
Tracking down these app remnants manually can be a hassle. With CleanMyMac, you can uninstall apps and clean up their supporting files completely. Plus, its Applications tool helps keep your programs updated with the latest security patches.
Old iOS backups
If you use your Mac to back up your iOS devices, you may end up with unnecessary old backups. If you no longer need them, you can safely remove them. You will find the steps on how to remove them via System Settings in our clearing guide.
Downloaded screen savers
Have you already tried the outstanding dynamic screen savers feature introduced in macOS Sonoma? But did you know that they are downloaded as video files and can take up more than 20GB of space? You can remove them and re-download them later if needed.
The Trash
This one may seem obvious, but emptying the Trash/Bin can significantly reduce the System Data volume on your Mac. The Trash/Bin usually becomes a graveyard of unnecessary files and apps even if you turn on the option of emptying it automatically.
Why System Data keeps increasing
Many users have noticed that Time Machine snapshots can cause System Data to grow. Usually, these snapshots are deleted automatically after 24 hours — only if Time Machine is running regularly, ideally every hour. If you suspect that snapshots are the issue, ways to check and remove them safely are covered in our clearing guide.
If cleaning up snapshots doesn’t help, try updating your Mac. Installing the latest macOS update can clear out old system files and refresh your System Data automatically.
Clean up system junk automatically
While it's possible to clear space manually, there's a much easier option: using CleanMyMac. This Mac cleaner makes it easy to remove caches, app leftover files, document versions, old system logs, and even Xcode junk, helping free up space for what’s important to you.
You don't need to dig through system files manually: CleanMyMac scans your entire storage and finds junk files scattered across your Mac that are either obsolete or no longer needed.
Hopefully, you're no longer wondering why "System Data" takes so much disk space on my Mac. Knowing what is actually in there is the first step to recovering some space. And if you need safe, step-by-step ways to delete System Data on Mac, check out our clearing guide.
Frequently asked questions about System Data on Mac
Why does System Data stay large even after I delete apps?
Deleting an app removes only the .app file; caches, logs, and support files remain in ~/Library until you clean them manually or with the help of a dedicated uninstaller and keep counting toward System Data.
What is the difference between "System" and "System Data" in Mac storage?
"System" is macOS itself, and so you cannot delete it. In some macOS versions, including Tahoe, it is named explicitly — macOS. "System Data" is user-generated junk like caches, backups, and temp files — everything that macOS could not file under another category.
Is it safe to delete System Data on Mac?
Not as a single deletable category, since System Data is a collection of files. Some files can be removed safely if you no longer need them, but nothing should be removed without review simply because it is included in System Data. The actual removal steps are covered in our clearing guide.