| Decimal (Finder, Apple's specs) | Binary (Terminal, Windows) |
|---|
Why the numbers differ
Since Mac OS X 10.6, Finder reports sizes in decimal units, the same way Apple and drive makers advertise them. Windows and many command-line tools use binary units, where each step is 1,024 rather than 1,000, but often still write "GB". By terabyte scale the gap is almost 10%.
On a Mac, df -h prints binary units as Gi, while Finder and System Settings print decimal GB.
Where the rest of your space went
Units explain a few percent. If your 512 GB Mac has far less free than you expect, the rest is usually caches, iPhone backups, Xcode data and old downloads. Broom shows which folders hold it and clears the safe part to the Trash.
Questions
Is a GB 1,000 or 1,024 MB?
Both are used. In decimal (SI) units a GB is 1,000 MB. In binary units the 1,024 version is properly called a GiB (gibibyte).
Does macOS use GB or GiB?
Finder and System Settings use decimal GB. Terminal's df -h and du -h use binary units, labelled Gi.
Why does my 1 TB drive show 931 GB on Windows?
Windows divides by 1,024³ and labels the result GB. 1 TB is 931.32 GiB.