Kilo is aunit prefix in themetric system of measurement, denoting multiplication by onethousand (103). TheInternational System of Units reserves thelowercase symbolk.
Kilo is derived from theGreek wordχίλιοι (chilioi), meaning "thousand".
In 19th century English the prefix was sometimes spelled chilio, in line with apuristic opinion byThomas Young.[1][2] As an opponent of suggestions to introduce the metric system in Britain, he qualified the nomenclature adopted in France as barbarous.
By extension, currencies are sometimes also preceded by the prefix:
For multiples of thebyte in some fields ofcomputer science and information technology, another definition has been in common use, in which thekilobyte measures 1024 bytes (210 bytes), because 210 is approximately 103. The reason for this application is that digital hardware natively usebase 2 exponentiation.
TheNational Institute of Standards and Technology (NIST) comments on the confusion caused by these contrasting definitions: "Faced with this reality, theIEEE Standards Board decided that IEEE standards will use the conventional, internationally adopted, definitions of the SI prefixes."[3] A new set ofbinary prefixes, based on powers of 2, was introduced by theInternational Electrotechnical Commission (IEC), which defines 1024 bytes as onekibibyte (1 KiB).
When units occur inexponentiation, such as in square and cubic forms, any multiplier prefix is part of the unit, and thus included in the exponentiation.
| Prefix | Base 10 | Decimal | Adoption [nb 1] | |
|---|---|---|---|---|
| Name | Symbol | |||
| quetta | Q | 1030 | 1000000000000000000000000000000 | 2022[1] |
| ronna | R | 1027 | 1000000000000000000000000000 | |
| yotta | Y | 1024 | 1000000000000000000000000 | 1991 |
| zetta | Z | 1021 | 1000000000000000000000 | |
| exa | E | 1018 | 1000000000000000000 | 1975[2] |
| peta | P | 1015 | 1000000000000000 | |
| tera | T | 1012 | 1000000000000 | 1960 |
| giga | G | 109 | 1000000000 | |
| mega | M | 106 | 1000000 | 1873 |
| kilo | k | 103 | 1000 | 1795 |
| hecto | h | 102 | 100 | |
| deca | da | 101 | 10 | |
| — | — | 100 | 1 | — |
| deci | d | 10−1 | 0.1 | 1795 |
| centi | c | 10−2 | 0.01 | |
| milli | m | 10−3 | 0.001 | |
| micro | μ | 10−6 | 0.000001 | 1873 |
| nano | n | 10−9 | 0.000000001 | 1960 |
| pico | p | 10−12 | 0.000000000001 | |
| femto | f | 10−15 | 0.000000000000001 | 1964 |
| atto | a | 10−18 | 0.000000000000000001 | |
| zepto | z | 10−21 | 0.000000000000000000001 | 1991 |
| yocto | y | 10−24 | 0.000000000000000000000001 | |
| ronto | r | 10−27 | 0.000000000000000000000000001 | 2022[1] |
| quecto | q | 10−30 | 0.000000000000000000000000000001 | |
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