How to clear System Data on Mac (safely, step by step)

There is no button that clears System Data on a Mac, and no folder to open, because System Data is a leftover category rather than a place. You shrink it by shrinking the real files counted into it, in this order: empty the Trash, delete old iPhone and iPad backups, erase deleted mail, turn on Optimize Mac Storage in Photos, and let macOS release its local Time Machine snapshots. Everything below is a setting Apple documents, done in System Settings or Finder. No Terminal.

If you want the conceptual version first, what System Data actually is covers what lives in the category and why macOS won't itemize it. This page is the procedure. Menu paths are Apple's own and apply to macOS Ventura 13 and later, which covers Sonoma, Sequoia and Tahoe.

First, write down the number you're starting from

Apple menu > System Settings > General > Storage. Give the bar chart a moment to finish calculating, then hover over the grey block. That figure is what you're trying to move, and you want it on paper, because half the steps below change what the Mac can do without changing what the chart says.

Treat it as approximate. Howard Oakley, who has taken this pane apart repeatedly, describes System Data as "not a real category, but an etcetera": macOS adds up everything it can attribute to Music, Photos, Documents and the rest, subtracts that from the space actually used, and calls the remainder System Data. His own Mac shows a Music folder of over 100 GB as under 50 GB in the Music category, and the missing half lands in System Data. So some of that grey block is not junk. It's arithmetic.

For a free-space figure you can trust, open Disk Utility instead, select the volume's container in the sidebar, and read the free space there.

The order that works

1. Empty the Trash. Apple's own documentation is blunt about this: moving a file to the Trash doesn't release its space until the Trash is emptied. Do this first, because it costs nothing and it makes every later measurement honest. While you're in Storage settings, the "Empty Trash automatically" recommendation erases anything that has sat in the Trash for more than 30 days, which stops this particular problem recurring.

2. Delete old iPhone and iPad backups. When one of these exists it is usually the largest single item in there, because a backup holds a copy of an entire phone and nothing ever deletes it. Connect the device, open Finder, click it in the sidebar, and under the General tab click Manage Backups. Right-click a backup and choose Delete. If the phone is long gone, Finder's Go > Go to Folder and ~/Library/Application Support/MobileSync/Backup/ gets you to the same folder. Whether it's safe to delete iOS backups covers what you give up.

3. Erase deleted and junk mail. In Mail, choose Mailbox > Erase Junk Mail, then Mailbox > Erase Deleted Items. Mail keeps deleted messages and their attachments on disk until you do, and on an account you've had for years the attachments are the heavy part. More on that in why Mail takes up so much space.

4. Turn on Optimize Mac Storage in Photos. Open Photos, choose Photos > Settings, click iCloud, tick iCloud Photos, then select Optimize Mac Storage. Full-resolution originals stay in iCloud and smaller copies live on the Mac. Two trade-offs: it consumes your iCloud plan, and you need a connection to pull an original back down. "Download Originals to this Mac" reverses it. How Optimize Mac Storage really behaves has the detail.

5. Let the local snapshots go. Time Machine saves a snapshot of your startup disk roughly every hour and keeps it for 24 hours, plus one of your last successful backup until space is needed. Those snapshots get counted into System Data even though Time Machine made them. Apple's documented way to clear them without Terminal: open Time Machine settings, click Options, set Backup Frequency to Manually, click Done, wait a few minutes, then turn automatic backups back on.

Read the next sentence before you bother. Apple also says your Mac counts snapshot space as available storage, and that snapshots don't occupy the space needed for downloading, copying or installing. So this step often shrinks the number without giving you anything you didn't already have. Local snapshots, explained and what purgeable space is cover why the disk lies to you here.

6. Use the More Info buttons macOS does give you. Back in Storage settings, several categories have a More Info button beside them, and those panes are the only itemized view Apple ships. Apple points at Applications, Documents, Messages, Music Creation, Podcasts, Trash and TV. Documents is the useful one for most people, since it lists large files and old downloads by size, which is where much of a full disk usually turns out to be.

7. If you need the space right now, boot into safe mode once. Apple documents this as a way to temporarily free space, because starting in safe mode clears certain system caches that macOS then recreates as needed. On Apple silicon: shut down fully, hold the power button until "Loading startup options" appears, select your volume, hold Shift and click Continue in Safe Mode. On Intel: restart and hold Shift until the login window. Restart normally to leave. Apple's own example is finishing a macOS update that won't otherwise fit.

The step to skip

Almost every article on this subject tells you to open ~/Library/Caches and empty it. It is the weakest step on this page, for two reasons.

Apple's storage documentation states that when space is needed, macOS itself clears caches and logs that are safe to delete, including temporary database files, interrupted downloads, staged macOS and app updates, and Safari website data. The system has already taken the easy wins. What remains is mostly data your apps rebuild the next time you open them, so you get a number that drops today and returns by Thursday, plus a slower first launch of everything.

The scale of the trade shows up in Apple's own forums. One user with 92 GB of System Data on a 245 GB MacBook Air emptied /Library/Caches/, /System/Library/Caches/ and /var/log by hand and recovered, in their words, "maybe 5GB". That is a lot of risk for five percent of the problem. Whether it's safe to delete cache on Mac and what you can safely delete go through which caches are actually worth touching.

Safari is the one exception, because its website data does get large: Safari > Settings > Privacy > Manage Website Data > Remove All. Apple warns that this signs you out of every site you were logged into, and that cost is the whole reason to think before clicking it.

If System Data is still over 100 GB

Once you've done the list and the number is still enormous, you are probably looking at one of two things.

It might be miscounting, as above, in which case no amount of deleting will move it and the free-space figure in Disk Utility is the one that matters. Or you have hit a bug. Users have reported single system caches running away and filling hundreds of gigabytes, notably the com.apple.mediaanalysisd cache and the CloudKit cache under com.apple.bird. Those are user reports rather than acknowledged defects, but the pattern is recognizable: one folder, absurdly large, growing on a schedule. Report that to Apple. Housekeeping won't touch it.

On a 256 GB machine this all bites harder, because the working margin is thinner to begin with. Read is 256 GB enough for a MacBook Air before you conclude the Mac is broken, and if you're already seeing warnings, start with startup disk almost full.

Expect a floor, not a zero

Some of System Data cannot be reduced, and any tool promising otherwise is selling you something. Swap files, the sleep image, the caches macOS is actively using, and the files it simply failed to categorize are all counted in there, and every one of them is either load-bearing or imaginary. A realistic goal is getting the number back to something proportionate, not making it disappear.

All of this is tedious mainly because macOS won't tell you what's inside the block. Plumby breaks System Data into named items instead: quiet caches, live caches, logs, swap, the sleep image, and the local snapshots with the date each one was taken. It offers only the items that are safe to remove, which means it will not delete your snapshots, your logs or your swap file at all, and it says so rather than pretending. Nothing goes until you open a review sheet and confirm it, and the space freed is measured as each file leaves rather than promised in advance.