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    SI Prefixes


    The abbreviation SI is from the French language name Système International d’Unités (also known as International System of Units).   Twenty SI prefixes are used to combine with units of measure.

    For example, the prefix name kilo, which equals 1,000 denotes a multiple of one thousand, as exemplified by:
    • 1 kilometer = 1,000 meters
    • 1 kilogram = 1,000 grams
    • 1 kilowatt = 1,000 watts
    Each SI prefix name has an associated symbol which can be used in combination with the symbols for units of measure.

    Accordingly, the “kilo” symbol, k, may be used to denote km, kg, and kW, for representing kilometer, kilogram, and kilowatt respectively. 

    SI prefixes are internationally recognized. The twenty SI prefixes are presented below:

    10n Prefix Symbol Decimal Equivalent
    1024 yotta- Y 1,000,000,000,000,000,000,000,000
    1021 zetta- Z 1,000,000,000,000,000,000,000
    1018 exa- E 1,000,000,000,000,000,000
    1015 peta- P 1,000,000,000,000,000
    1012 tera- T 1,000,000,000,000
    109 giga- G 1,000,000,000
    106 mega- M 1,000,000
    103 kilo- k 1,000
    102 hecto- h 100
    101 deca- da 10
    10−1 deci- d 0.1
    10−2 centi- c 0.01
    10−3 milli- m 0.001
    10−6 micro- µ 0.000 001
    10−9 nano- n 0.000000001
    10−12 pico- p 0.000000000001
    10−15 femto- f 0.000000000000001
    10−18 atto- a 0.000000000000000001
    10−21 zepto- z 0.000000000000000000001
    10−24 yocto- y 0.000000000000000000000001