No hard disk shows proper free space cause the vendors lie about it and we've all come to accept this as "standard".
A one terabyte (1 TB) disk drive would be expected to hold around 931 GB or 953,674 MB.
Humans think in base 10, computers in base 2 .... "back in the day", a GB was 1,024 MB. Since the marketing types and bean counters realized that by using base 10, they can change 931 into 1,000 we have been seeing this HD sizes reported this way.
Same reason why booze is sold in "5ths", a 1 pound size box of pasta only has 14.5 ounces in it, and a "pint size" container of OJ now only has 14.5 ounces in it.
I thought it was because the HDD Supplier state the unformatted specifications as the size of the drive. Then when the drive is formatted then the size is actually less then what the drive was sold as. The same was true for Floppy Disk. Unformatted they are about 2 MB. Formatted they are 1.44 MB. Literal physical space is lost at Format.