File Size Converter (KB, MB, GB, TB)

What this calculates

File sizes are confusing because there are two competing standards: 1 KB = 1,024 bytes (binary, historical) vs 1 KB = 1,000 bytes (decimal, SI standard). Storage manufacturers use decimal (which makes drives look bigger), operating systems use binary. This converter handles both so you can settle the gap between what your hard drive claims and what Windows reports.

Formula & how it works

Binary (KiB, MiB, etc.): each step ×1024. 1 KiB = 2^10 bytes; 1 MiB = 2^20; 1 GiB = 2^30; 1 TiB = 2^40. Decimal (KB, MB, etc., SI prefixes): each step ×1000. 1 KB = 10^3 bytes; 1 MB = 10^6; 1 GB = 10^9. The two start to diverge at GB scale (~7 %), grow to ~10 % at TB scale.

Worked example

A 1 TB hard drive claims 1,000,000,000,000 bytes (decimal). Windows shows 931 GB because Windows uses binary: 1,000,000,000,000 / 2^30 = 931.3 GiB. Not a defect — just two definitions. A 500 MB MP3 file in iTunes (decimal) shows as 477 MiB in Linux (binary), same exact file.

Frequently asked questions