Finder, Storage settings and Wombit can show three different numbers for the same disk, and none of them is wrong. They count different things. These are the differences the app accounts for, and how it shows each one.
Why the numbers differ
- Purgeable space
- Finder counts space macOS can free when it needs to, such as cached iCloud files and local snapshots, as available. A large copy can still fail before macOS frees it.
- Local snapshots
- Time Machine keeps snapshots on the disk itself. They hold space no folder shows, which is why deleting files sometimes frees nothing.
- APFS clones
- A copied file can share its blocks with the original. Adding up file sizes counts that space twice; the app counts a fully shared clone once.
- Sparse files
- Docker's disk image can report a size far larger than the space it takes. The app shows both: the size the file says, and the space on disk.
- Hard links
- One file under two names still takes its space once, so it's counted once.
- System Data
- Storage settings puts caches, logs, snapshots and developer files under one number. The app splits it into named buckets and says how much it couldn't explain.
Read more
The guides explain each of these from macOS's side, with what the system itself offers: