|Yes, it the difference between binary and decimal counting.|
In Binary 1 kB is 1024 bytes.
In Decimal 1 kB is 1000 bytes.
Manufactures use the decimal counting system as it makes the disk look bigger than it actually is but the computer uses digital counting because it is a digital computer.
So for every kB you will lose 24 bytes and there are a lot of kBs in 500 GB. 500,000 if my maths is correct. Multiply that by 24 and you get 12,000,000 which is 12 Gbs.
Add to that the over heads for formatting and there is where your space has gone, You will always lose something when formatting as there are overheads that do not show up in space available.