Data units: MB vs MiB, GB vs GiB
Why does a disk show less capacity than advertised? The difference between decimal (MB, GB) and binary (MiB, GiB) data units explained.
Why a disk “shows less”
Manufacturers state capacity in decimal units (1 GB = 10⁹ B), while operating systems often display binary ones (1 GiB = 2³⁰ B) – and the gap grows with size.
| Sold as | Exact bytes | System shows |
|---|---|---|
| 256 GB | 256,000,000,000 | 238.4 GiB |
| 500 GB | 500,000,000,000 | 465.7 GiB |
| 1 TB | 1,000,000,000,000 | 931.3 GiB |
| 2 TB | 2,000,000,000,000 | 1.82 TiB |
It is not a defect or “stolen” space – just two different prefix systems. Windows historically labels GiB as “GB”; macOS and Linux now count in decimal.
Decimal vs. binary prefixes
| 1 gigabyte (GB) GB to GiB | = | 0.93132257 gibibytes |
| 1 gibibyte (GiB) GiB to GB | = | 1.0737418 gigabytes |
| 1 megabyte (MB) MB to MiB | = | 0.95367432 mebibytes |
| 1 terabyte (TB) TB to GiB | = | 931.32257 gibibytes |
Bits and bytes
| 1 byte (B) bytes to bits | = | 8 bits |
| 1 megabyte (MB) MB to Mb | = | 8 megabits |
| 1 gigabyte (GB) GB to MB | = | 1000 megabytes |
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