This has actually started to become a source of confusion. In data processing, traditionally the kilo-, mega-, giga-, tera-, etc., extensions were powers of 1024, not 1000 (1, 2, 3, 4, etc., respectively), although recently there seems to be a push to force these to be used in the SI (metric) respect of being powers of 1000. This results in a difference of 24 bytes per K, 48,576 bytes per M, 73,741,824 bytes per G, etc.

According to the IEC International Standard definitions (1998), the units we traditionally think of KB, MB, GB, TB, etc., are now technically KiB, MiB, GiB, TiB, etc.

So the number you were thinking was 1024, although you managed to be correct both in actual number you suggested, and in your thought about another value.