Kibibyte (KiB)

A kibibyte (KiB) is exactly 1024 bytes. Defined by the IEC in 1998 as the unambiguous binary alternative to “kilobyte”, which had historically meant either 1000 or 1024 bytes depending on context. The mismatch is one of computing’s most persistent sources of confusion.

The full series of binary prefixes:

• KiB (kibi) = 2¹⁰ = 1,024 bytes
• MiB (mebi) = 2²⁰ = 1,048,576 bytes
• GiB (gibi) = 2³⁰ ≈ 1.07 × 10⁹ bytes
• TiB (tebi) = 2⁴⁰ ≈ 1.10 × 10¹² bytes
• PiB (pebi) = 2⁵⁰

In practice usage is split:

• Hard drive manufacturers: use the decimal prefixes (KB = 1000, GB = 10⁹). A “1 TB” drive holds 10¹² bytes, which Windows reports as “931 GB” because Windows uses binary GB (= GiB).
• Linux/macOS file systems: increasingly use the IEC prefixes (KiB, MiB).
• Windows file system: uses KB/MB/GB to mean 1024-based but with the SI prefix names — the source of the discrepancy users notice.
• RAM: always binary. 16 GB of RAM is 16 GiB; the “G” is loose terminology.
• Network rates: always decimal. 100 Mbps is 100 × 10⁶ bits/sec, not 100 × 2²⁰.

The pragmatic rule: when precision matters, use the IEC prefix (KiB, MiB) explicitly. For casual use, “KB” and “MB” are usually fine — but be aware which convention your tool is using when a number doesn’t quite match.