Mac System Data is 100+ GB: how to find what is using it

A System Data bar of 100 GB or more is nearly always caused by one or two things, not by everything at once. The goal is to find those, not to wipe every cache.

1. Restart and wait

Restart the Mac, then check Storage again after a few minutes. The figure is calculated lazily and often shows stale numbers. Purgeable caches and some temporary files are cleared on restart.

2. Check Time Machine snapshots

If you use Time Machine, local snapshots can take tens of GB. In Terminal run:

tmutil listlocalsnapshots /

See how to delete them if the list is long.

3. Look at iPhone and iPad backups

Each device backup is commonly 5–40 GB. See how to review and remove old ones.

4. Developer data

If you have ever installed Xcode, ~/Library/Developer can hold 20–60 GB of Derived Data, simulator runtimes and device support files. See the Xcode guide. Docker Desktop also keeps a single disk image that can reach tens of GB.

5. Find big folders yourself

In Terminal, this lists the largest folders in your home directory (it can take a minute):

du -sh ~/Library/* 2>/dev/null | sort -rh | head -15

Only remove something once you know what it is. If a folder name is unfamiliar, search for it first.

Or let a scanner show you

McCleaner does steps 2–4 for you: it scans these locations for free, groups them into Safe, Caution and Advanced with a plain explanation for each, and selects nothing by default. Cleaning is the paid part.

Disclosure: this guide is published by the developer of McCleaner. Scanning is free; cleaning is paid, from €1.99. Back up important data before deleting anything. Commands are provided as is.