the number is real. it is also not all yours to gain.

purgeable space: what a cleaner counts that you already had

macOS keeps a category of files it can delete at any moment without asking: local Time Machine snapshots, cached iCloud files whose originals are in the cloud, and blocks held for copy-on-write that nothing needs any more. this is purgeable space, and macOS frees it automatically the moment the disk gets tight.

which means it is already yours. if you need twenty gigabytes for a video export, macOS will make twenty gigabytes. a scan that counts this as reclaimable is not lying — deleting it does free the space today — but it reports a gain you were never going to be denied.

purgeable space is also the reason the biggest bar on the Storage screen refuses to add up: what «system data» is actually using

how much purgeable space is actually there

on the Mac these numbers came from — a 994.66 GB data volume, 96 % full — purgeable space was 6.60 GB. two thirds of one per cent of the disk, and about a seventh of what was free: not nothing, and not the headline either.

the figure is a subtraction. macOS answers «how much room is there» twice: once counting blocks free right now, once counting what it could give an app that really needs the space. the gap between the two is the purgeable space — here 52.19 GB minus 45.59 GB.

Apple's documentation for that second number is explicit that it counts purgeable resources: volumeAvailableCapacityForImportantUsageKey

why the command line will not show you

the usual advice is to check in Terminal, so it is worth knowing what that gets you. three tools, same volume, one minute apart: df -k said 45.59 GB free, diskutil info /System/Volumes/Data said 45.6 GB of container free space, system_profiler SPStorageDataType said 45.63 GB. they agree to within rounding — and not one mentions purgeable space.

one detail is worth stating plainly, because it circulates as fact: diskutil info has no «Purgeable Space» field. not in its normal output, not in its property-list form — grepping both for the word returns nothing. guides that tell you to read purgeable space out of diskutil are describing a field that does not exist.

the difference lives in an API rather than in anything you can type. Howard Oakley has tracked how inconsistently macOS reports this, and after three years his conclusion is that it has got worse.

his 2026 write-up of where the tools disagree, and of the contradiction in Apple's own docs about snapshots: eclecticlight.co — aren't snapshots purgeable?

no Time Machine, no snapshots — and still purgeable space

snapshots are the category everyone names first, and the tmutil documentation does class them as purgeable. but they exist only if Time Machine has run. on the machine measured here tmutil destinationinfo answers «No destinations configured», and tmutil listlocalsnapshots /System/Volumes/Data prints an empty list — zero snapshots, and 6.60 GB of purgeable space regardless.

check the data volume, not the short form: tmutil listlocalsnapshots / is what most guides quote, and it reports on a different volume. never set up a backup destination, and both come back empty — the snapshots explanation is not about your Mac.

caches: real space, and why it comes back

every app you use keeps a cache, and on a Mac a few years old the total is genuinely large. deleting it does free the space. two things get lost in the presentation.

where an app keeps its cache depends on how it was installed — a sandboxed build puts everything inside its own container instead: the App Store version versus the one from the site

• caches exist to make things fast. removing them makes the next launch of everything slower while they rebuild, and a month later the disk is full again anyway.
• they come back. a browser cache deleted today is several gigabytes again by next week. this is the category that makes a cleaner feel necessary on a schedule.
• and a caution that matters more than the size: some apps keep cache and data in one folder. a messenger's twenty gigabytes are mostly downloaded media that is also your message history, and only that app's own cleanup knows which half is disposable.

the narrow version is always worth doing: clear one app's cache, usually the browser, usually when something is misbehaving.

where a Mac cleaner actually works

• old iOS and iPadOS backups, in ~/Library/Application Support/MobileSync/Backup. tens of gigabytes each, one per device, kept forever. remove them from Finder's device screen, not by hand.
• installers you never deleted — .dmg and .pkg files in Downloads, on the Desktop, in Documents. dull, and often the single largest honest number in the report.
• developer files, if you have Xcode. simulators and build products run to tens of gigabytes and nothing else on this list comes close.
• the Trash, which is more often the answer than anyone expects.

leftovers of apps you removed

the per-app version of this, for when you are removing something rather than auditing everything: uninstall an app with its leftovers

this is the category people are told about most and can check least, so it deserves a measurement. the Mac used for the numbers above has 165 folders in ~/Library/Application Support and 518 application bundles installed. matching the two lists and then checking the results by hand left 17 folders belonging to software no longer on the disk: 2.28 GB in total, the largest 941 MB, the oldest untouched since March 2022. one had been left behind by a cleaning app that was itself uninstalled years ago.

the point is not the size. nobody finds these by browsing: the folders are named after vendors rather than apps, and they sit among 148 others in active use.

nor is automatic matching the whole answer. the same pass flagged 109 folders before checking: 20 were macOS services, others live software under an unfamiliar name — «Blackmagic Design» is DaVinci Resolve, «obs-studio» is OBS. matching by name alone over-reports, which is why the list matters more than the total.

these categories are where a cleaner earns its keep, and they are also the ones you can look at yourself in ten minutes. nothing here needs an app; what an app gives you is one pass and a sort by size.

how to judge any Mac cleaner

• does it show what it will remove, item by item, before removing it? a number with a button is not a report.
• does it delete, or move to the Trash? the failure mode of cleaning is removing something you needed, and that should cost a restore rather than a file.
• does it say what it deliberately left alone, and why? a tool that reports success on everything is telling you less, not doing more.
• does it separate purgeable space from real gain? this is the sharpest question on the list, and a single headline number cannot answer it.
• what does it need access to before it can see any of this? nothing reads ~/Library or another app's container without full disk access, so the question is not whether it asks but whether what it asks for matches the job.
• and the general one: does it promise to make the Mac faster? disk space and speed are different problems. the overlap is narrow — a nearly full disk hurts performance because swap has nowhere to go, and that is the only honest version of the claim.

how to reason about a utility asking for broad access, panel by panel: why a Mac app asks for accessibility permission

the swap case has a symptom you can check rather than guess at, and it is a memory reading, not a disk one: what memory pressure actually measures

for the record on our side: hop has a cleanup section in its uninstall module, it works down the same list, it moves everything to the Trash rather than deleting it, and it names what it is leaving alone. it is also not the point of the app, and if the only thing you need is one folder emptied, the Storage screen and ten minutes will do it for nothing.

what that module does and does not touch: the uninstaller in hop

the baseline to judge all of it against — Apple's own instructions for freeing space, notable for what they leave out: purgeable space is not mentioned once. Apple Support — free up storage space on Mac

frequently asked questions

do Mac cleaner apps actually free space?

yes, the files are real. part of what they count is purgeable space macOS would have released on its own when the disk got tight, so the gain is smaller than the headline. on the Mac measured here that part was 6.60 GB.

what is purgeable space?

files macOS can delete at any moment without consequence — local snapshots, cached cloud files, blocks held for copy-on-write. it counts as used on the Storage screen and is released automatically when something needs the room.

how do i check purgeable space in Terminal?

you cannot read it directly. df, diskutil and system_profiler all report the same free-space figure and none breaks out purgeable space. it is the difference between plain free space and the capacity macOS reports as available for important usage — an API value, not a command.

does diskutil show purgeable space?

no. diskutil info has no purgeable space field, in either its normal or its property-list output. it reports container free space, which is the same figure df gives.

is it safe to delete caches?

generally yes, and they are rebuilt. the exception is apps keeping cache and data in one folder, where the pile includes things you want to keep.

will cleaning make my Mac faster?

only in one case: a disk so full that swap has no room, which produces real slowdowns and memory warnings. otherwise free space and speed are unrelated.

can i do it without an app?

yes. System Settings → General → Storage for the overview, Finder's device screen for old device backups, Downloads and the Desktop for installers, ~/Library for the caches. one afternoon rather than one button.