Mac storage full for no reason? Why the numbers don't add up

Why your Mac's storage numbers disagree

You check System Settings, then Finder, then a disk app, and get three different answers. Usually none of them is wrong. Each one counts something slightly different, and APFS, the file system on every modern Mac, has features that make simple adding up unreliable.

Below are the reasons the numbers drift apart, roughly from most to least common.

1. Purgeable space is counted as free in one place

Purgeable space is space that files use now but macOS can free on its own, mostly local Time Machine snapshots and caches it can rebuild. Apple's older System Information guide notes that space can be available and used at the same time. System Settings counts it as available. Terminal's df and Disk Utility's free figure count it as used. On a Mac with a lot of purgeable space, that alone can explain a big gap. Purgeable space on a Mac explains what's in it.

2. Local snapshots keep files you deleted

With automatic backups on, Time Machine saves a snapshot of your disk about every hour and keeps it for 24 hours, plus one of your last successful backup until space is needed. A snapshot keeps the old versions of everything that changed after it was made. So when you delete a large file, the space doesn't really come back until the snapshots that hold it are gone. Apple's snapshot article says your Mac counts snapshot space as available, which is why System Settings may look fine while an app still can't find room. Time Machine local snapshots shows how to list and remove them.

3. The Trash and Recently Deleted

Moving something to the Trash doesn't free its space. Apple's free up storage article says so plainly: the space becomes available only when you empty the Trash. The same goes for the Recently Deleted album in Photos, where Apple says deleted photos and videos stay for 30 days unless you remove them sooner (Photos guide). Mail keeps deleted messages in its Trash mailbox until they're erased.

4. APFS clones: copies that share space

When you copy a file on the same APFS volume, macOS can make a clone. Apple's APFS documentation describes a clone as a copy that takes no extra space on disk; changes are written elsewhere, and both files keep sharing the parts that didn't change.

That has two effects. Every copy shows its full size in Finder, so adding up folders counts the shared data twice. And deleting one copy frees almost nothing, because the other copy still uses the same blocks.

5. Compression and sparse files

Some files take up less space than their size. macOS compresses many of its own files and some app files, and Finder's Get Info window shows both numbers, the size and the space on disk. Sparse files, such as disk images and virtual machine disks, have empty regions that take no space at all; Apple's documentation explains that blocks are allocated only when they're written. A tool that adds up file sizes and one that adds up space on disk will give different totals for the same folder.

6. Hard links

A hard link lets one file appear in two places while it's stored once. Time Machine backup disks formatted as Mac OS Extended rely on them heavily, and some apps and command-line tools create them too. The du manual says it counts a file with several hard links only once per run, but if you add up two folders separately, it's counted in both.

7. Files you can't see

Some space is real but out of view:

• Other people's files. Storage settings has an Other Users & Shared category for files other accounts on the Mac created or share. You can't open their home folders, so you can't measure them.
• Folders macOS protects. Without Full Disk Access, apps can't read Mail, Messages or Safari data, among others. Apple's Privacy & Security guide lists what that permission covers. You grant it in System Settings, then Privacy & Security, then Full Disk Access.
• Folders only macOS can read. The Spotlight index, document version history and other system data can't be measured by any app.

Much of this hidden space ends up in the System Data category. System Data on a Mac explains what's in it and what you can do about it.

8. Volumes, units and Terminal

Your startup disk is an APFS container holding several volumes that share one pool of free space: macOS itself, your data, and small volumes for startup, recovery and swap. In Terminal, df -H / reports only the read-only macOS volume, so its Used column looks tiny. Your files are on the Data volume.

Units differ too. Apple's capacity article explains that storage makers count 1 GB as one billion bytes, and macOS does the same. df -h and du -h count in powers of 1,024, so their figures look about 7% smaller. Use -H with df to match System Settings.

How to check it yourself

These steps clear up the common causes first, then compare figures that measure the same thing. If you're not sure where each number lives, how to check storage on a Mac walks through System Settings, Finder, Disk Utility and Terminal.

1. 1

   Empty the Trash and Recently Deleted

   Check the Trash, then choose Finder > Empty Trash. In Photos, check the Recently Deleted album under Utilities, where deleted photos stay for 30 days.

2. 2

   Restart your Mac

   macOS lets go of its swap files at restart, which returns the space they were using.

3. 3

   Check for local snapshots

   In Terminal, run tmutil listlocalsnapshots /. Snapshots keep files you deleted until they're removed, usually within a day.

4. 4

   Compare like with like

   In Disk Utility, choose View > Show All Devices and look at your startup disk's container. In Terminal, run df -H /System/Volumes/Data. Both show free space without purgeable space.

5. 5

   Measure what you can see

   In Finder, select your home folder and the Applications folder and press Command-I to see their sizes. Compare the total with the used space in Storage settings: the rest is macOS itself, other users' files, local snapshots and data only macOS can read.

The two Terminal commands from the steps, both read-only:

df -H /System/Volumes/Data

tmutil listlocalsnapshots /

To measure your own home folder from Terminal, which counts hard links once and reports space on disk:

du -sh ~ 2>/dev/null

Without Full Disk Access for Terminal, some folders in your Library can't be read and are left out. The figure is in powers of 1,024.

What's safe to do and what isn't

Safe: emptying the Trash and Recently Deleted once you've checked them, restarting, and removing local snapshots when your Time Machine backups are current.

Not worth it: deleting one copy of a cloned file to save space, since the other copy keeps the space in use. Filling the disk with a large file to force macOS to purge, which can leave you with a full startup disk if anything goes wrong. And removing files from /private/var or other system folders because the numbers don't match: what's there is macOS's working data, and rm skips the Trash.

How MacClearings counts your disk

Breakdown was made for this question. It starts from the volume figures macOS reports, the same ones System Settings uses, then measures the folders behind them. Its scanner counts allocated size, the space files actually use, so compressed files, sparse files and clones are measured as they really are. Files with several hard links are counted once.

Where cloned files share space with copies elsewhere, Breakdown says how much it's leaving out so nothing is counted twice. If the folders still add up to more than the disk holds, it says by how much and why. And whatever it can't measure is shown as its own number under "What MacClearings can't see", with the likely reasons: local snapshots, the Spotlight index and document versions, folders that need Full Disk Access, and files changed since the last scan. It doesn't hide the gap or guess.

Breakdown only reads. When you decide to make room, Suggestions and the other views stage items for review, MacClearings moves what you confirm to the Trash, and History can undo it. That space comes back when you empty the Trash, which MacClearings never does for you. Duplicates never reports clones or hard links as duplicate files, since removing them wouldn't free anything.