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What is purgeable space on a Mac, and how to get it back

Updated 13 October 2026 · Krishan Assi

Short answer. Purgeable space is storage your Mac is using right now but can free by itself when it needs the room: mostly Time Machine local snapshots, copies of iCloud files it can download again, and caches. Finder and Storage settings count it as available, while df and some installers count only what's empty this minute, which is why the numbers disagree. To get it back, empty the Trash, connect your backup drive and let Time Machine finish, and if you need the space now, ask Time Machine to thin its snapshots with tmutil thinlocalsnapshots /. If nothing is complaining about space, you can leave it alone.

What purgeable space means

Apple describes purgeable space as space that macOS can free up when needed by removing files, and says you can't remove those files yourself, because macOS removes them as needed (Apple). Apple also says available storage includes free space plus purgeable disk caches, so the same space can be "available" and "used" at the same time (Apple).

Apple doesn't publish a full list of what counts. These are the usual parts:

What Why macOS can free it
Time Machine local snapshots Time Machine saves one about every hour and keeps each for 24 hours, plus one of your last backup until space is needed. Apple says your Mac counts snapshot space as available (Apple).
iCloud Drive files With Store in iCloud on, your Mac keeps only recently opened files when space is needed. The rest stay in iCloud (Apple).
Caches and leftovers When space is needed, macOS clears temporary database files, interrupted downloads, staged macOS and app updates, Safari website data and more (Apple).

Snapshots are often the biggest part. A snapshot is a frozen copy of your disk at one moment, so a large file you delete stays on disk until the snapshots holding it are gone.

Why Finder, Storage settings and df disagree

Each tool answers a slightly different question.

Where you look What it shows
Finder (select Macintosh HD, then File > Get Info, or the status bar) Available, which Apple says can include purgeable space
System Settings > General > Storage Used and available, worked out over time, so the figure can shift while you watch
Disk Utility Used, Purgeable (when there is some) and Free as separate figures
df -h / in Terminal Only space that's physically empty right now

To see your own purgeable figure:

  1. Open Disk Utility from Applications > Utilities.
  2. Select your startup disk in the sidebar, usually Macintosh HD.
  3. Read the figures under the bar. If Purgeable is large, the gap between Finder and df is mostly that.

df counts in units of 1,024 rather than Finder's 1,000, so its figures also look about 7% smaller.

Don't expect every number to match exactly. Testing by Howard Oakley at Eclectic Light found that Finder and Storage settings don't always reflect purgeable space correctly, and that macOS didn't always free it when it should have (Eclectic Light). Disk Utility was the most consistent of the three.

Why apps say there isn't enough space

You can see 80 GB available in Finder and still get a "not enough space" message. There are two common reasons.

The app checks the wrong number. Apple tells developers to check a figure that includes space macOS can free when the user asks for something, such as a download they've chosen (Apple Developer). Some apps and installers, often older or cross-platform ones, check only what's empty right now, which is the smaller df figure.

macOS doesn't free it in time. Purging happens when something writes to the disk and runs short. It isn't instant, and in Oakley's tests it sometimes didn't happen at all. A big copy or install can fail before the space appears.

In both cases, the fix is to turn purgeable space into free space before you start. The steps below do that.

How to get purgeable space back safely

Do these in order and check Disk Utility after each one. Most people only need the first three.

1. Empty the Trash

Anything in the Trash still takes space until you empty it (Apple). Click and hold the Trash in the Dock, then choose Empty Trash.

2. Let Time Machine catch up

If you use Time Machine with an external drive, connect it and let a backup finish. The snapshot of your last backup is kept until the next one succeeds, so a drive that's been away for weeks can hold a lot.

3. Use Apple's recommendations

Choose Apple menu > System Settings > General > Storage, and look at Recommendations. Store in iCloud lets your Mac drop local copies of older iCloud files. Optimize Storage removes Apple TV films and shows you've watched and keeps only recent mail attachments. Empty Trash Automatically removes items after 30 days (Apple). These make more of your files purgeable over time; they don't free space instantly.

4. Thin or delete Time Machine local snapshots

This is the step that frees the most space quickly. Snapshots are a safety net: they let you get back files from the last day before they reach your backup drive. Removing them is permanent.

First, list them. This only reads:

tmutil listlocalsnapshots /

Names starting com.apple.TimeMachine. are Time Machine's. Names starting com.apple.os.update- belong to macOS updates; leave those alone. macOS doesn't show how much space each snapshot holds.

Without Terminal, Apple's own method is to pause automatic backups (Apple):

  1. Choose Apple menu > System Settings > General > Time Machine.
  2. Click Options, choose Manually from Backup Frequency, then click Done.
  3. Wait a few minutes for the local snapshots to be deleted.
  4. Set Backup Frequency back to what it was. Don't forget this step, or Time Machine stops backing up on its own.

In Terminal, the gentlest option asks Time Machine to thin its own snapshots, by its own rules:

tmutil thinlocalsnapshots /

According to man tmutil, you can add an amount in bytes and an urgency from 1 to 4, for example tmutil thinlocalsnapshots / 20000000000 4 to try to reclaim about 20 GB. Time Machine still decides which snapshots go. If you get a permissions error, put sudo in front and enter your administrator password.

To delete one snapshot, use its date from the list:

sudo tmutil deletelocalsnapshots 2026-10-08-093015

sudo tmutil deletelocalsnapshots / deletes every Time Machine local snapshot on your startup disk at once. Only do that if your backup drive is up to date.

5. Restart

A restart clears swap files (where macOS puts memory overflow) and some temporary files, and it's a cheap thing to try before a big install. It won't reliably free snapshots or iCloud copies, so do it after the steps above, not instead of them.

6. Give it a day

Hourly snapshots expire after 24 hours by themselves. If you've just deleted a lot and nothing is urgent, waiting a day is often all you need.

What not to do

Don't use fill-the-disk tricks. You'll find advice to create a huge dummy file, or copy something big over and over, until macOS panics and purges everything. It sometimes works, but it's risky:

  • If macOS doesn't purge fast enough, and testing shows it sometimes doesn't, the disk reaches zero. Apps can quit or fail to save, and you can lose unsaved work.
  • A Mac whose startup disk is completely full can behave badly and may struggle to start up.
  • It throws away your snapshot safety net and the offline copies of your iCloud files in one go.
  • If the dummy file is left behind, you've used the space you were trying to free.

Thinning snapshots does the same job in a controlled way.

Also avoid anything that tells you to turn off System Integrity Protection, delete folders from Recovery mode, or run sudo rm on system folders. One wrong path can stop your Mac starting up. If the space is in System Data rather than purgeable, read why System Data gets so large instead.

When to leave it alone

Purgeable space isn't a problem in itself. macOS uses it to keep your recent changes recoverable and your iCloud files close at hand. Leave it if:

  • you have plenty of free space even without it
  • nothing has refused to install, copy or save
  • the figure goes up and down over a day or two, which is snapshots coming and going as normal

Act only when you need real free space now, such as before a macOS update, a large download or a video export.

How DiskFox shows purgeable space

We make DiskFox, a storage app for Mac. It saves you checking Disk Utility and Terminal:

  • Home shows what's free right now, and when macOS reports more than 1 GB of purgeable space, a line underneath says how much you'd have once macOS clears it. In Settings you can switch the big number to "Available, like Finder" instead.
  • The System Data page counts Time Machine and macOS update snapshots and says plainly that macOS doesn't tell apps their size. Its Let Time Machine Thin Them… button asks Time Machine to thin its snapshots, after a confirmation that explains what they're for. DiskFox never picks or deletes a snapshot itself; Time Machine decides.

DiskFox has no visual disk map, measures only your startup disk, checks only while it's open, and needs macOS 14 or later. It's a one-time purchase with a 14-day free trial and no card needed. What DiskFox shows about System Data has more detail.

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