When you need this conversion
Explaining the “missing” space on a new drive, sizing a cloud volume listed in GiB, or setting a virtual machine’s disk. Cloud providers such as AWS and Google Cloud often bill storage in GiB, so converting avoids surprises.
Two definitions
In 1998 the IEC introduced separate names for binary sizes:
- kilobyte (kB) = 1,000 bytes; kibibyte (KiB) = 1,024 bytes
- megabyte (MB) = 10⁶ bytes; mebibyte (MiB) = 2²⁰ bytes
- gigabyte (GB) = 10⁹ bytes; gibibyte (GiB) = 2³⁰ bytes
The gap grows with each prefix: 2.4% at kilo, 4.9% at mega, 7.4% at giga, 10% at tera.
Drive sizes as Windows shows them
- 256 GB = 238.4 GiB
- 500 GB = 465.66 GiB
- 1,000 GB = 931.3 GiB
- 2,000 GB = 1,862.6 GiB
Common mistakes
Thinking the drive is faulty. The bytes are all there; only the unit changed.
Using GiB numbers against GB limits. A 100 GiB file won’t fit a 100 GB volume: it’s 107.4 GB.