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What is purgeable space on Mac, and why does System Data not shrink?

Updated 2026-10-21

Quick answer: purgeable space is disk space macOS counts as free when it needs it: caches, iCloud files kept locally, local snapshots. You cannot delete it by hand. macOS frees it automatically. That is why free space differs between Finder, Storage settings and Terminal.

What counts as purgeable

The exact list is macOS's decision, but it typically includes:

  • Cached data that macOS or apps have marked as removable.
  • iCloud Drive files kept on the Mac while Optimize Mac Storage is on. macOS can remove the local copy and keep the file in iCloud.
  • Time Machine local snapshots, which macOS thins out when it runs low on space.

Where you can see it

In Finder select your disk, choose File → Get Info (Command-I) and look at Available. On many macOS versions the purgeable part is shown in brackets next to it. Storage settings uses the same idea when it draws its bar.

Terminal shows the lower-level view:

df -h /System/Volumes/Data
diskutil info / | grep -E "Container (Total|Free) Space"

These two commands agree with each other but not with Storage settings, because of units. On a test Mac df reported 460 GiB total and 86 GiB available, while diskutil reported 494.3 GB total and 92.3 GB free. That is the same disk: df counts in GiB (1024³ bytes) and macOS Settings counts in GB (1000³ bytes), and 494.3 GB is 460 GiB.

Why System Data does not shrink when you delete things

  • Storage settings recalculates in the background, so it can lag behind what you just removed.
  • Purgeable space is only freed when macOS needs it, so deleting something that was already counted as purgeable changes nothing right away.
  • Snapshots and caches are counted in System Data, so they move the number only when they are really removed.

What you can do about it

  • Do not try to force it. macOS frees purgeable space before an update or a big download.
  • Free real space instead: clear app caches, Xcode leftovers and old local snapshots.
  • Wait a few minutes and reopen Storage settings, or restart the Mac, before judging the result.

What not to do

Do not install tools that promise to empty purgeable space. There is nothing to empty by hand, and the one Terminal command with a similar name, purge, only clears the memory disk cache.

How See Your Disk treats it

See Your Disk reads the figure macOS calls available for important usage, which includes purgeable space, so its idea of used space matches the one macOS uses. Whatever no folder explains is shown as its own System Data block. To measure that yourself, see what is inside System Data.

See Your Disk
A map of your Mac's disk, and a safe way to clean it.
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Frequently asked questions

Can I delete purgeable space myself?

Not directly. Purgeable space is something macOS frees on its own when it needs room, for example for a large download or an update. What you can do is remove real files, such as caches, which gives you space immediately.

Why does Finder show more free space than Terminal?

Finder's Available figure includes purgeable space. Low-level tools such as df usually report only the space that is free right now, so they can show less.

Is purgeable space part of System Data?

Some of it can be, for example local snapshots and caches. Storage settings does not break purgeable space out by category, so treat the two as overlapping rather than separate.

Does the purge command empty purgeable disk space?

No. The purge command in Terminal flushes the disk cache held in memory. It does not free disk space and it does not empty purgeable space.

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