KB vs KiB — Decimal and Binary Data Units
Last updated February 14, 2026 · Data Storage
Digital storage is quoted in two incompatible families of units. Decimal (SI) units count in powers of 1,000: 1 kB = 1,000 bytes. Binary (IEC) units count in powers of 1,024: 1 KiB = 1,024 bytes. The gap compounds with each step — 7.4% at kilo, 10% at giga, and 10% again at tera.
Why your drive looks smaller than advertised
Manufacturers sell drives in decimal units, so a 1 TB drive really holds 1,000,000,000,000 bytes. Windows reports storage in binary units but labels them 'GB', so the same drive displays as roughly 931 GB — which is properly written 931 GiB. Nothing is missing; the two labels simply count differently.
Comparison
| Decimal (SI) | Binary (IEC) |
|---|---|
| 1 kB = 1,000 B | 1 KiB = 1,024 B |
| 1 MB = 1,000,000 B | 1 MiB = 1,048,576 B |
| 1 GB = 10⁹ B | 1 GiB = 1,073,741,824 B |
| 1 TB = 10¹² B | 1 TiB = 1,099,511,627,776 B |
Bits versus bytes
Broadband speeds are quoted in megabits per second (Mbps) while file sizes are in megabytes (MB). One byte is 8 bits, so a 100 Mbps connection transfers at most about 12.5 MB per second.