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The SI prefixes provide a convenient way to apply a decimal scale factor to a unit of measurement. For example, 1000 meters is a kilometer (km). However, the SI prefixes are frequently misused to apply a binary scale factor that happens to be close to a decimal factor.

For example, 1024

bytes is often incorrectly called a kilobyte (kB). Strictly speaking, a kilobyte is exactly 1000 bytes (because the SI prefix kilo denotes a factor of 1000).

The IEC (International Electrotechnical Commission) has standardized a set of binary prefixes. These prefixes can be used to unambiguously specify quantities which by their nature are most easily measured using binary scale factors.

Definitions

Examples

2 KiB, or 2 kibibytes, is the same as 2048 bytes
1 Mi bit, or 1 mebibit, is the same as 1048576 bits

Notes

The prefixes pebi and exbi are not in common use.

Reference

IEC 60027-2, Second edition, 2000-11, Letter symbols to be used in electrical technology—Part 2: Telecommunications and electronics.

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