What is purgeable space on a Mac, and is it really free?

By EgeTech LTD · October 6, 2026 · 2 min read

Open System Settings → General → Storage or the disk’s Get Info window and you may see a figure for available space, and somewhere a number marked purgeable. They are connected, and the difference explains why your Mac and your Terminal give you two different answers.

What purgeable means

Some of the files on your disk exist only to make things faster or to save you a download. macOS calls them purgeable because it can delete them whenever it needs the room, and rebuild or fetch them again if you need them. Typical examples:

• Files kept on the Mac only as a cache, for example items from iCloud Drive that also live in the cloud when “Optimize Mac Storage” is on.
• Caches and temporary files that the system manages.

You do not need to clean these by hand. The moment an app asks for more space than is free, macOS frees purgeable files to make it.

Two numbers for free space

That is why the Terminal can say 51 GB while Finder says 56 GB. Neither is wrong; they answer different questions. “How much can I use right now without anything being deleted?” is the df answer. “How much can I use, counting what macOS will reclaim for me?” is Finder’s.

To see the first one:

df -h /

Which number should you trust?

For deciding whether you can install a 10 GB Xcode runtime, the Finder number is the useful one: macOS will make room by purging if it has to. For understanding why a cleanup freed less than you expected, look at both. If df moved and Finder did not, you freed empty space that purgeable space was already covering.

For developers: how an app reads it

If you write macOS software and want the same figure Finder shows, ask for the capacity “for important usage” rather than the raw available capacity:

let values = try URL(fileURLWithPath: "/")
    .resourceValues(forKeys: [.volumeAvailableCapacityForImportantUsageKey])
let freeBytes = values.volumeAvailableCapacityForImportantUsage

The plain volumeAvailableCapacityKey returns only the empty part, which is the df number.

Does purgeable space matter for your cleanup?

Yes, in one way: the files you delete yourself are the ones macOS cannot purge for you, such as developer caches, old simulators and old projects. Those are the ones worth cleaning. See the full developer checklist.

If your storage looks stuck after a cleanup, read why the storage can stay full after deleting files.