You're seeing two different values because macOS's Finder reports GB, while df
reports GiB. Both numbers refer to the same actual number of Bytes.
You can use different bases to specify a large number of Bytes:
- 1 GB = 1 Gigabyte = 1000^3 Bytes (“Giga” is a so-called SI prefix)
- 1 GiB = 1 Gibibyte = 1024^3 Bytes (“Gibi” is a so-called binary prefix)
The former has been primarily used by hard drive vendors, and Apple has chosen to report the disk size in Finder in the same way as you'd get when you buy a drive. This is technically correct, as drives are sold in “GB” and “TB”.
The df
shipped with macOS instead shows your drive with binary prefixes, thus with a total capacity of 233 GiB (which is roughly equivalent to 250 GB).
PS: The GNU df
shipped with Linux will show binary prefixes when using df -h
, but labeling them as G
. If you want to use SI prefixes there, you have to use df -H
.