What is purgeable space on a Mac, and can you clear it?

What counts as purgeable

macOS marks data as purgeable when it can be removed without losing anything, either because another copy exists or because it can be created again.

• Local Time Machine snapshots, which keep earlier versions of your disk for about a day.
• Local copies of files in iCloud Drive, when Optimize Mac Storage is on. The original stays in iCloud.
• Full-size photos and videos, when iCloud Photos is set to Optimize Mac Storage.
• Films and TV programmes from Apple that you have already watched and can download again.
• Caches that apps have marked as safe for the system to remove.

Where to see it

Select your startup disk in Finder, usually Macintosh HD, and choose File, then Get Info. The Available line shows the total, with the purgeable part in brackets after it.

Disk Utility shows the same thing. Select the volume in the sidebar and read the Available figure, which also names the purgeable amount.

The Storage screen in System Settings does not show purgeable space as its own row. The data is counted under whichever category it belongs to, and snapshots are counted in System Data.

Why free space looks different in every tool

Finder and Disk Utility report available space as truly free space plus purgeable space, because from your point of view both can be used. Terminal reports only blocks that are free at this moment.

The command below shows that stricter figure for your data volume. It only reads. If the Avail column is much lower than what Finder shows, the gap is your purgeable space.

Neither number is wrong. Finder answers the question of how much you could store. Terminal answers the question of how much is unused right now.

df -h /System/Volumes/Data

When purgeable space becomes a problem

Most apps ask macOS for room in a way that triggers the purge, so you never notice. Problems appear with tools that read free blocks directly and refuse to continue.

• Disk partitioning tools, including Boot Camp Assistant on Intel Macs.
• Virtual machine and container apps that reserve a large disk image in advance.
• Some installers and games that check free space before they start.
• Large copies made with command-line tools.

How to free it when you really need to

First try the ordinary route: restart the Mac, then start the task again. macOS often purges what it can when a real request for space arrives.

If the purgeable space is mostly snapshots, you can ask macOS to thin them. The command below asks the system to release up to 20 GB from local snapshots at the highest urgency, oldest first. What you lose is the ability to restore files as they were at those moments without your backup drive. Backups already on your Time Machine drive are not affected.

For iCloud files, you can release individual downloads yourself. In Finder, right-click a file or folder in iCloud Drive and choose Remove Download. The item stays in iCloud and its icon shows a cloud. Do this only when the upload has finished.

tmutil thinlocalsnapshots / 20000000000 4

What not to do

Do not turn off Time Machine or iCloud to make the purgeable figure disappear. Turning off iCloud Drive or iCloud Photos can make the Mac download everything again or remove local copies, and turning off Time Machine removes your safety net. The purgeable space was not costing you anything.

Avoid the trick of filling the disk with a huge dummy file to force a purge. It can leave the Mac with no working room at all if it is interrupted, and tmutil does the same job safely.

How Diskzy shows it

Diskzy maps the whole disk and breaks System Data into named parts, each sized and labelled. Snapshots are marked Managed by macOS, so you can tell how much of a large System Data figure will come back without any action from you, and how much is caches, logs or developer data that you can clear.

Diskzy does not delete snapshots. For the parts you can act on, the Clean up tab lists each item with a reason, and removals go to the Trash.