Startup Disk Full on Mac? How to See What's Using Space and Free It Up

Published ✓ Verified ⏱️ 2 min read May 20, 2025 · by Ryan Bennett

Your Mac warns that the startup disk is almost full or your disk is almost full, apps slow down, and updates won’t install.

Why: macOS needs free space to run, swap memory and install updates. When the disk fills up, the usual culprits are large media files, old downloads, app caches and a full Trash. macOS has a built-in Storage view to show what’s using space and tools to recover it.

Fix 1: See what’s using your storage

macOS Ventura 13 or later: Apple menu > System Settings > General > Storage.
Earlier macOS: Apple menu > About This Mac > Storage.

The bar breaks storage down by category (Apps, Documents, System Data, and so on) and lists recommendations you can act on directly.

Fix 2: Empty the Trash and clear Downloads

Moving a file to the Trash doesn’t free space until you empty it — Control-click the Trash in the Dock > Empty Trash.
Open your Downloads folder (Finder > Go > Downloads) and delete installers and files you no longer need.
In Mail, clear large stored messages with Mailbox > Erase Junk Mail and Mailbox > Erase Deleted Items.

Fix 3: Delete or offload large files

Delete music, movies and podcasts you can stream or re-download later.
Move large photo or video libraries to an external drive.
Turn on Optimize Storage / Store in iCloud from the Storage screen so your Mac uses iCloud to free space automatically when it’s running low.
Compress files you rarely use (Control-click > Compress), then expand them when needed.

Fix 4: Clear system caches with safe mode

To temporarily recover space — useful right before a macOS update — start in safe mode, which clears certain system caches that are recreated as needed.

Apple silicon (M-series): Shut down, press and hold the power button until “Loading startup options” appears, select your disk, then hold Shift and click Continue in Safe Mode.
Intel: Restart and immediately press and hold Shift until the login window appears.

Restart normally to exit safe mode.

FAQ

What is “System Data” and can I delete it? It’s caches, logs and system files. Don’t delete it manually — empty the Trash, restart, and use safe mode (Fix 4) to let macOS clear caches safely.

How much free space do I need for an update? Leave several GB free beyond the installer download. If an update still says there isn’t enough space, free more and see macOS update won’t install.

Sources: Apple Support — Free up storage space on Mac · Apple Support — Start up your Mac in safe mode