Bytes / 1024 = kibibytes/kilobytes
Bytes / (1024*8) = mibibytes/megabytes
And for anyone wondering, yes, the official international standard has been changed so that a kilobyte is 1000 bytes, megabyte = 1000000 bytes, etc. which is stupid, but I don't think the BOS has amended the syllabus, and I hope they don't