Purgeable space on Mac, explained.

What is purgeable space on Mac?

Some files on your Mac exist for convenience. They can be recreated, or downloaded again, so macOS marks them as purgeable: it may delete them, without asking, when it needs the room. Purgeable space is the total of those files. The idea arrived in macOS Sierra in 2016, alongside the storage recommendations Storage settings still shows.

On a typical Mac, three things make up most of it:

• Local Time Machine snapshots. Hourly snapshots of your disk, kept between backups. They can hold tens of gigabytes of files you've already deleted.
• Downloaded iCloud files. With Optimize Mac Storage on, the copies of iCloud Drive files on your Mac can be removed and downloaded again later.
• Caches. Some caches, from apps and from macOS itself, are marked as safe to delete under pressure.

macOS doesn't publish a list of what it counts, and it doesn't show you one either.

Why Finder counts purgeable space as available

Finder and Storage settings show available space as free space plus purgeable space. That's on purpose: if you copy a big file, macOS makes room by purging, so in practice the space is yours. Terminal's df shows only what's free right now. To see both:

df -h /System/Volumes/Data

Then compare its Avail column with Finder: choose Go › Computer, select Macintosh HD, and press Command-I. On the Mac this guide was written on, df showed 32 GB available while macOS counted 270 GB available for important files. That's about 235 GB of purgeable space, with no Time Machine snapshots on the disk at all.

How macOS reclaims it

When an app asks for more space than is free, a background service in macOS deletes purgeable files until there's enough, starting with what's least useful. Local snapshots go oldest first, iCloud downloads are removed, and caches are cleared. It usually happens within seconds, and you won't see it.

Time Machine's own tool shows the mechanism. tmutil thinlocalsnapshots takes an amount to reclaim and an urgency from 1 to 4, which is how macOS asks for space with more or less force.

How to clear purgeable space on Mac

Most of the time, don't. It's already counted as free, and deleting it early only means downloading or rebuilding those files sooner. Clear it when a tool reads raw free space and refuses to run, like a large installer, a virtual machine asking for a fixed-size disk, or a script that checks df.

1. Restart. Temporary files and swap are cleared, and macOS takes the chance to purge.
2. Delete local Time Machine snapshots. They're usually the biggest part. List them, then delete by date:

   tmutil listlocalsnapshots /
   tmutil deletelocalsnapshots 2026-10-05-093012

   Time Machine local snapshots has every command and what each removes.
3. Remove iCloud downloads. In iCloud Drive, Control-click big files or folders and choose Remove Download. See iCloud Drive taking up space.

What you can't do is empty purgeable space with a single button. macOS doesn't offer one. Apps that promise to remove it usually fill the disk with a temporary file until macOS purges, which macOS would have done anyway the moment you needed the room.

Where local snapshots fit in

On a Mac that backs up with Time Machine, snapshots are often most of the purgeable space, and also the part that makes System Data look huge in Storage settings. They're also the only part you can list and delete by name. If your purgeable number grows overnight and drops after a backup, snapshots are why. For the rest of System Data, see what is System Data on Mac.