Sizes

Logical size, size on disk, and why the totals differ.

Logical size

What a file would hold if it were fully downloaded and uncompressed. Finder shows this number in Get Info as the first figure.

Size on disk

The space a file actually occupies right now. Cloud files that are not downloaded, sparse disk images and cloned copies take far less than their logical size. SpareDisk shows an on-disk hint whenever a file occupies less than half its size. The View menu and Settings switch every list, map and total to sizes on disk.

Why totals differ

The volume bar counts everything on the disk. A location counts only what is inside it. System files, other users, snapshots and folders you have not added as locations make up the rest. Hard links are counted once, as du does.

Choosing a basis

Use logical size to understand what your files contain. Use size on disk to understand what removing them would free. SpareDisk keeps both for every item, so switching is instant.

Questions not covered here: [email protected].