Digital storage & data: the exact defined values
1 GB = 1 000 000 000 bytes under SI, but 1 GiB = 1 073 741 824 bytes — a 7.4% gap that explains 'missing' drive space.
How the base unit is defined
A byte is 8 bits. Multiples split into two systems: decimal SI prefixes (kB = 1000 B) and binary IEC prefixes (KiB = 1024 B).
Exact values table
"Exact" means the value is fixed by definition and carries no measurement uncertainty.
| Quantity | Exact value | Notes |
|---|---|---|
| 1 kilobyte (kB, SI) | 1000 bytes | Used by drive manufacturers and network speeds. |
| 1 kibibyte (KiB, IEC) | 1024 bytes | Used by operating systems and RAM. Open converter → |
| 1 megabyte (MB, SI) | 1000000 bytes | 10⁶ bytes. |
| 1 mebibyte (MiB, IEC) | 1048576 bytes | 2²⁰ bytes. Open converter → |
| 1 gigabyte (GB, SI) | 1000000000 bytes | 10⁹ bytes — what the box on a hard drive means. |
| 1 gibibyte (GiB, IEC) | 1073741824 bytes | 2³⁰ bytes — what Windows reports and labels 'GB'. Open converter → |
Rounding traps that actually change your result
Why a 1 TB drive shows as 931 GB
The manufacturer sells 1 000 000 000 000 bytes (SI terabyte). Windows divides by 1024 three times and calls the result GB, giving 931.32. No storage is missing — the two systems simply label the same bytes differently. macOS and Linux now report in SI units, so the same drive shows as 1 TB there.
Network speeds are bits, not bytes
A 100 Mbps connection moves 100 megabits per second, which is 12.5 megabytes per second at best. The lowercase b is bits; the uppercase B is bytes.
Where these values come from
- IEC 80000-13
Defines the binary prefixes kibi, mebi, gibi and tebi.
- NIST: Prefixes for binary multiples
NIST guidance on when to use SI versus IEC binary prefixes.
Frequently asked questions
Is 1 GB 1000 MB or 1024 MB?
Both labels are in use. Under SI, 1 GB = 1000 MB = 1 000 000 000 bytes. Under IEC, 1 GiB = 1024 MiB = 1 073 741 824 bytes. Storage manufacturers use SI; Windows uses the binary values while printing 'GB'.
Why does 16 GB show as less than 16 GB?
Because the device is measured in SI gigabytes (16 000 000 000 bytes) and the operating system displays gibibytes, giving about 14.9. Formatting and system files then take a further share.
Convert digital storage & data now
These converters use the exact factors listed above.