Standard Prefixes for Units of Measurements

These tables of unit prefixes are derived from tables published by the National Institutes of Science and Technology. Consult for further information.

" The 11th CGPM (1960, Resolution 12) adopted a first series of prefixes and symbols of prefixes to form the names and symbols of the decimal multiples and submultiples of SI units. Prefixes for 10-15 and 10-18 were added by the 12th CGPM (1964, Resolution 8), those for 1015 and 1018 by the 15th CGPM (1975, Resolution 10), and those for 1021 ,1024, 10-21,and 10-24 were proposed by the CIPM (1990) for approval by the 19th CGPM (1991). "
-- NIST Special Publication 330, 1991 Edition

SI prefixes
Factor   Name  Symbol
10008 1024   yotta Y
10007 1021   zetta Z
10006 1018   exa E
10005 1015   peta P
10004 1012   tera T
10003 109   giga G
10002 106   mega M
10001 103   kilo k
10002/3 102   hecto h
10001/3 101   deka
or deca
Factor   Name  Symbol
1000-1/3 10-1   deci d
1000-2/3 10-2   centi c
1000-1 10-3   milli m
1000-2 10-6   micro µ
1000-3 10-9   nano n
1000-4 10-12   pico p
1000-5 10-15   femto f
1000-6 10-18   atto a
1000-7 10-21   zepto z
1000-8 10-24   yocto y

Also, from,
In December 1998 the International Electrotechnical Commission (IEC), the leading international organization for worldwide standardization in electrotechnology, approved as an IEC International Standard names and symbols for prefixes for binary multiples for use in the fields of data processing and data transmission. The prefixes are as follows:

Binary-multiple prefixes
Factor   Name  Symbol   Meaning Derived from:
260   exbi Ei   exabinary: (210)6 exa: (103)6
250   pebi Pi   petabinary: (210)5 peta: (103)5
240   tebi Ti   terabinary: (210)4 tera: (103)4
230   gibi Gi   gigabinary: (210)3 giga: (103)3
220   mebi Mi   megabinary: (210)2 mega: (103)2
210   kibi ki   kilobinary: (210)1 kilo: (103)1


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."

It is important to recognize that the new prefixes for binary multiples are not part of the International System of Units (SI), the modern metric system. However, for ease of understanding and recall, they were derived from the SI prefixes for positive powers of ten. As can be seen from the above table, the name of each new prefix is derived from the name of the corresponding SI prefix by retaining the first two letters of the name of the SI prefix and adding the letters "bi," which recalls the word "binary." Similarly, the symbol of each new prefix is derived from the symbol of the corresponding SI prefix by adding the letter "i," which again recalls the word "binary." (For consistency with the other prefixes for binary multiples, the symbol Ki is used for 210 rather than ki.)

Official publication
These prefixes for binary multiples, which were developed by IEC Technical Committee (TC) 25, Quantities and units, and their letter symbols, with the strong support of the International Committee for Weights and Measures (CIPM) and the Institute of Electrical and Electronics Engineers (IEEE), were adopted by the IEC as Amendment 2 to IEC International Standard IEC 60027-2: Letter symbols to be used in electrical technology - Part 2: Telecommunications and electronics. The full content of Amendment 2, which has a publication date of 1999-01, is reflected in the tables above and the suggestion regarding pronunciation.