Purgeable space, and why deleting files frees nothing

You empty the Trash after removing a large folder, look at the storage bar, and nothing has changed. Nothing is broken and the files really are gone. The space is being held as purgeable, which means macOS is counting it as used until it has a reason to release it.

What purgeable actually means

Purgeable is space the system believes it can reclaim on demand but has not yet reclaimed. It is made of two things, and the proportions matter because only one of them is worth acting on:

• Local snapshots. Time Machine keeps hourly snapshots of the volume on the volume itself, so a file removed an hour ago still exists inside a snapshot.
• Cached content macOS can fetch again, such as iCloud files already uploaded and downloadable copies of media.

The design is deliberate and mostly helpful: when an application genuinely needs space, macOS releases purgeable space automatically. The frustration is that it will not do it just because you are looking at a number.

Seeing how much of it is snapshots

This is the useful measurement, and it takes one command:

tmutil listlocalsnapshots /

Each line is one snapshot, with the date and time it was taken in the name. A Mac backing up hourly will typically hold around twenty four of them, and together they can account for tens of gigabytes on a drive where a lot has changed recently.

Making the space come back now

Snapshots expire on their own, usually within a day. If you need the space before then, ask the system to thin them rather than deleting them one by one:

tmutil thinlocalsnapshots / 20000000000 4

That asks for roughly 20 GB back, with an urgency of 4, which is the level that will remove snapshots rather than merely trying. Raise the number for more space. The command reports each snapshot it removes.

Why the numbers disagree everywhere

Purgeable is the single biggest reason the free space figure differs between places on the same Mac. Finder tends to count it as available because it can be reclaimed. The storage bar in System Settings tends to count it as used because right now it is. Both are honest, and they are answering different questions.

It also explains the specific case of a Mac that is full immediately after an update, which has its own guide: disk full after a macOS update.

When purgeable is not the answer

If snapshots come back tiny and the space still has not returned, the files were not where you thought. Start from the storage bar, which will at least tell you the category, and then look at that category by actual file size.