What Is Purgeable Space on Mac and How to Clear It

Your Mac says it has 120 GB available, yet a 12 GB installer refuses to run. The gap is purgeable space — storage macOS counts as available because it could free it, but hasn't actually freed yet. Here's what's inside that number, why apps don't trust it, and how to make macOS let go of it now.

What macOS counts as purgeable

Purgeable space is data macOS is willing to sacrifice the moment something else needs the room. Three things make up almost all of it:

• Local Time Machine snapshots. When Time Machine is on, macOS keeps hourly APFS snapshots of your startup disk. They can hold many gigabytes of changed and deleted files, and every byte of them counts as purgeable.
• Evicted iCloud content. With Optimize Mac Storage enabled, files already uploaded to iCloud Drive and full-resolution photos can be dropped from the local disk on demand, so macOS treats their local copies as disposable.
• Regenerable caches. System and app caches that macOS knows it can rebuild — font caches, Spotlight working files, streamed media — are marked purgeable too.

To see the split, open Disk Utility, select Macintosh HD, and read the Available figure: something like "120.4 GB (38.2 GB purgeable)". Finder's Get Info window folds purgeable into its single "available" number, which is why Finder and your installer often disagree about how much room you really have.

Why installers complain when space looks free

Purgeable space is a promise, not free space. The bytes are still physically on disk; macOS frees them lazily, only when disk pressure gets high enough. Installers — macOS updates especially — check how much space is genuinely free right now, and some abort rather than trust the system to purge mid-install. That's how you end up staring at "not enough disk space" on a Mac that reports 100 GB available.

Left alone, macOS will purge on its own as the disk fills. But if you need the room this minute, you can force its hand.

Thin Time Machine snapshots

Local snapshots are usually the biggest purgeable item and the easiest to clear:

# see which local snapshots exist
tmutil listlocalsnapshots /

# thin snapshots, reclaiming as many bytes as possible (urgency 4 = most aggressive)
sudo tmutil thinlocalsnapshots / 999999999999 4

The second command deletes snapshots until it has reclaimed the number of bytes you passed — an oversized number means "free as much as you can." There is no undo for a deleted snapshot, but the stakes are low: your real backups on the Time Machine drive are untouched, macOS resumes taking hourly snapshots immediately, and local snapshots expire after about 24 hours anyway.

Evict iCloud copies and force a purge

If Optimize Mac Storage is on, you can hand back space deliberately: right-click a file in iCloud Drive and choose Remove Download. The file stays safe in iCloud, and the local copy disappears. To undo, right-click the file again and choose Download Now.

As a last resort, you can trigger the purge macOS keeps postponing. Duplicate a large file in Finder (select a big video and press Cmd-D a few times) until free space gets genuinely low, give macOS a minute to react, then delete your copies and empty the Trash. Disk pressure forces the purge, and the space you see afterwards is real. It's crude, but it needs no third-party tools, and the only things you delete are the temporary copies you just made.

Watch the real number, not the promise

When you're judging free space, trust Disk Utility's breakdown over Finder's single figure. And if the disk keeps filling back up, find out what's actually consuming it — our guide to seeing what's taking up space on your Mac walks through the storage breakdown, folder-size views, and free visualizers.