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May 10, 2026 · 4 min read

Why your Mac says storage is full when it isn't

macOS reports 'Disk Almost Full' even when most files are in caches and leftovers. Here's what's actually using the space and how to find out.

You open About This Mac, see the angry red disk gauge, and the obvious user content — photos, documents, downloads — only accounts for a fraction of what's used. Where is the rest?

The macOS storage UI hides almost everything

The Apple-menu storage view groups storage into broad categories: Documents, Applications, Photos, Mail, System, Other. The "System" and "Other" buckets are where the actual problem usually lives. Those two buckets can easily be 100–200 GB on a Mac that has been in use for a year.

What lives in System / Other:

  • All cache directories (browser, system, app)
  • Application support data for apps you have installed and uninstalled
  • Time Machine local snapshots (yes, even when not actively backing up)
  • Mail database (can be 30+ GB)
  • iOS device backups
  • Xcode derived data and simulator state
  • Logs

macOS does not give you tools to break this down by directory.

How to actually see where the storage went

There are three honest ways:

  1. Terminal: du -sh ~/Library/*/ | sort -h shows you the size of each top-level Library subdirectory. The biggest entries are where to start.
  2. Finder Get Info: Right-click a folder → Get Info to see size. Slow on big folders because Finder calculates recursively.
  3. A dedicated tool: Unclutter scans the right directories and ranks findings by size in 10–30 seconds, then offers cleanup.

The biggest reclaim opportunities

In the order they typically pay off:

  1. Browser caches — 20–50 GB
  2. App leftovers from uninstalled apps — 10–50 GB
  3. Xcode derived data and simulators (developers only) — 50–100 GB
  4. Old Time Machine local snapshots — 5–30 GB
  5. Mail attachments — 5–20 GB

If you handle the top two of these, the storage warning usually goes away.

Want the one-click version?

Unclutter does everything in this guide in 30 seconds.