everyday mac tools

The Mac says storage is full, but the folders do not add up

· 5 min read

If the Mac says the disk is full and adding up your folders gets you nowhere near the number, nothing is broken. Finder is only showing you the parts of the disk you own and can see, and a full disk is usually full of things that are neither.

The missing space is almost always in one of six places: hidden Library folders, Time Machine local snapshots, other user accounts, other volumes sharing the same container, files that were deleted while an app still had them open, or space macOS is holding as reclaimable. Work through them in that order.

Start with two honest numbers

Before hunting, find out how big the gap really is.

Select your startup disk in the Finder sidebar (or on the Desktop), then File, Get Info. The Available line is the one macOS believes. If it says something like “42 GB available (20 GB purgeable)”, note both figures.

Then open Terminal and run df -h /System/Volumes/Data. That is the volume your files actually live on; / is the sealed system volume and its numbers will look wrong if you read them as your disk.

If those two disagree, the difference is purgeable space, and purgeable space on a Mac explains why it does not release itself just because you want it to. If they agree and your folders still do not add up, keep going.

Make Finder count properly

Finder does not calculate folder sizes by default, so a list view with a Size column full of dashes is not evidence of anything.

Open a Finder window, View, Show View Options, and turn on Calculate all sizes. Give it a minute on a large folder. Then sort by size and work from the top.

Two folders it will not show you at all:

  • ~/Library, hidden by default. Hold Option and open the Go menu; Library appears in the list.
  • Everything outside your home folder. Press Command-Shift-Period in a Finder window to reveal hidden items, then look at the disk root.

~/Library is where the surprises live: application support folders, containers, caches, mail, and any app that keeps a local copy of something large. On many Macs it is the biggest folder the owner has never opened.

Measure from the top down in Terminal

Faster than clicking, and it sees things Finder skips.

  1. sudo du -xhd 1 /System/Volumes/Data | sort -h lists the top level of your data volume smallest to largest. The -x stops it wandering onto other mounted volumes.
  2. Take the largest line and repeat one level down: sudo du -xhd 1 /System/Volumes/Data/Users | sort -h, and so on.
  3. du -sh ~/Library/* for your own Library.

Two things to know. Permission errors are normal and can be ignored. And APFS lets two files share the same blocks, while du counts both at full size, so totals can read higher than reality. Use it to rank, not to audit.

The four places Finder will never show you

Time Machine local snapshots. macOS keeps hourly snapshots of your data on the internal drive so you can restore without the backup disk. Run tmutil listlocalsnapshots /. If that prints a list, you have space tied up in it, and Time Machine local snapshots covers how to thin them safely.

Other user accounts. You cannot read another account’s home folder, so nothing you do in Finder will ever account for it. On a shared Mac this is frequently the whole answer: one person’s photo library or downloads folder is using half the disk and is invisible to everyone else. sudo du -shx /Users/* will give you the totals.

Other volumes in the same APFS container. Free space on an APFS disk is shared. Run diskutil apfs list and look at every volume in your container, not just Macintosh HD. Developer machines routinely accumulate simulator and virtual machine volumes here, each consuming real gigabytes that appear nowhere in your home folder.

Deleted files that are still open. If an app had a file open when it was deleted, the space is not released until that process quits. Run sudo lsof +L1 and look at the SIZE column. A log file that a crashed process is still holding can be enormous, and a restart clears the lot.

If you would rather see all of that as one list, Crumb audits the whole Mac rather than just your home folder: the System Data breakdown, local snapshots, iOS backups, swap, and a per-account view showing which user on a shared Mac is using the space. The audit itself is read-only and free, so it is a reasonable way to find the gap even if you clean up by hand afterwards.

The ordinary suspects, checked quickly

Once you know roughly where the weight is, these five take a couple of minutes and account for a surprising share of full disks:

  1. Trash, everywhere. Your Trash, the Trash on any external drive, and Photos’ Recently Deleted album, which holds items for 30 days.
  2. Downloaded macOS installers. An Install macOS <name> app is usually 12 to 15 GB.
  3. iPhone and iPad backups, in ~/Library/Application Support/MobileSync/Backup.
  4. Downloads. Not because it is glamorous, but because disk images and installers pile up there for years.
  5. Mail attachments, if you use Mail with large mailboxes stored locally.

When the number still will not settle

Restart. Not as folklore: local snapshot accounting, cache reclamation and the storage figure in System Settings all update lazily, and a restart forces most of it.

Then give it an hour before you check again. The storage bar in System Settings, General, Storage is calculated in the background and lags behind reality, sometimes considerably. Deleting 40 GB and immediately seeing the same number does not mean the deletion failed.

If after a restart the disk is genuinely full and you have accounted for everything, the honest answer may be that the Mac is too full to work with rather than mysteriously full. What System Data is on a Mac covers the category that swallows most of the difference.

Questions

Finder says 60 GB available but I cannot save a 2 GB file. Check how much of that 60 GB is purgeable. Some operations, particularly installers and disk image creation, ask for real free space and will refuse before macOS reclaims anything.

Why is my system volume showing as nearly full? It is not your volume. / is a sealed, read-only snapshot of macOS itself and it is meant to be almost entirely used. Read /System/Volumes/Data instead.

Is it safe to run du with sudo? Yes. du only reads directory sizes; it does not change anything. The sudo is there so it can read folders your account cannot.

Do I need to boot into Recovery to see the real numbers? No. Everything above works from a normal login. Recovery is for repairing a disk, not for measuring one.