(SI Prefixes Table, IEC Prefixes for binary multiples) SI Prefixes Table
The International System of Units, universally abbreviated SI (from the French Le Système International d’Unités), is the modern metric system of measurement.
The 20 SI prefixes used to form decimal multiples and submultiples of SI units are:
Symbol | Name | Factor | Symbol | Name | Factor | |
---|---|---|---|---|---|---|
Y | yotta | 10^{24} | y | yokto | 10^{-24} | |
Z | zetta | 10^{21} | z | zepto | 10^{-21} | |
E | exa | 10^{18} | a | atto | 10^{-18} | |
P | peta | 10^{15} | f | femto | 10^{-15} | |
T | tera | 10^{12} | p | pico | 10^{-12} | |
G | giga | 10^{9} | n | nano | 10^{-9} | |
M | mega | 10^{6} | µ | micro | 10^{-6} | |
k | kilo | 10^{3} | m | milli | 10^{-3} | |
h | hecto | 10^{2} | c | centi | 10^{-2} | |
da | deka | 10^{1} | d | deci | 10^{-1} |
It is important to note that the kilogram is the only SI unit with a prefix as part of its name and symbol. Because multiple prefixes may not be used, in the case of the kilogram the prefix names of Table are used with the unit name “gram” and the prefix symbols are used with the unit symbol “g.” With this exception, any SI prefix may be used with any SI unit, including the degree Celsius and its symbol °C.
Example: 357 000 mm = 35 700 cm = 357 m = 0.357 km (m = meter)IEC Prefixes for binary multiples
Because the SI prefixes strictly represent powers of 10, they should not be used to represent powers of 2. Thus, one kilobit, or 1 kbit, is 1000 bit and not 2^{10} bit = 1024 bit. To alleviate this ambiguity, prefixes for binary multiples have been adopted by the International Electrotechnical Commission (IEC) for use in information technology since December 1998.
Symbol | Name | Factor | Origin | Derivation |
---|---|---|---|---|
Ki | kibi | 2^{10} | kilobinary: (2^{10})^{1} | kilo: (10^{3})^{1} |
Mi | mebi | 2^{20} | megabinary: (2^{10})^{2} | mega: (10^{3})^{2} |
Gi | gibi | 2^{30} | gigabinary: (2^{10})^{3} | giga: (10^{3})^{3} |
Ti | tebi | 2^{40} | terabinary: (2^{10})^{4} | tera: (10^{3})^{4} |
Pi | pebi | 2^{50} | petabinary: (2^{10})^{5} | peta: (10^{3})^{5} |
Ei | exbi | 2^{60} | exabinary: (2^{10})^{6} | exa: (10^{3})^{6} |
It is suggested that in English, the first syllable of the name of the binary-multiple prefix should be pronounced in the same way as the first syllable of the name of the corresponding SI prefix, and that the second syllable should be pronounced as “bee.”
Examples and comparisons with SI prefixes:
1 Kibit = 2^{10} bit = 1024 bit
1 kbit = 10^{3} bit = 1000 bit
1 MiB = 2^{20} B = 1 048 576 B
1 MB = 10^{6} B = 1 000 000 B
1 GiB = 2^{30} B = 1 073 741 824 B
1 GB = 10^{9} B = 1 000 000 000 B