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SI prefixes and their etymologies

SI prefixes

PrefixSymbolFactorOrdinary Notation*Name
yottaY10241 000 000 000 000 000 000 000 000septillion
zettaZ10211 000 000 000 000 000 000 000sextillion
exaE10181 000 000 000 000 000 000quintillion
petaP10151 000 000 000 000 000quadrillion
teraT10121 000 000 000 000trillion
gigaG1091 000 000 000billion
megaM1061 000 000million
kilok1031 000thousand
 
hectoh102100hundred
dekada10110ten
 
1001one
 
decid10-10.1tenth
centic10-20.01hundredth
 
millim10-30.001thousandth
microμ10-60.000 001millionth
nanon10-90.000 000 001billionth
picop10-120.000 000 000 001trillionth
femtof10-150.000 000 000 000 001quadrillionth
attoa10-180.000 000 000 000 000 001quintillionth
zeptoz10-210.000 000 000 000 000 000 001sextillionth
yoctoy10-240.000 000 000 000 000 000 000 001septillionth
*The “ordinary notation” column uses spaces to separate numbers into groups of three digits. In the US, commas are more often used for this purpose, but spaces have the advantage of avoiding confusion when numbers might be seen by readers who use the comma as the decimal point.

SI prefix etymologies

PrefixPronunciationOrigin
yottaYOTE-uh or YOTT-uhLatin: “eight” [(103)8]
zettaZETT-uhLatin: “seven” [(103)7]
exaEX-uhGreek: “six” [(103)6]
petaPET-uhGreek: “five” [(103)5]
teraTAIR-uhGreek: “monster”
gigaJIG-uh or GIG-uhGreek: “giant”
megaMEG-uhGreek: “big”
kiloKILL-ohGreek: “thousand”
hectoHECK-toeGreek: “hundred”
dekaDECK-uhGreek: “ten”
 
deciDESS-ihLatin: “tenth”
centiSENT-ihLatin: “hundredth
milliMILL-ihLatin: “thousandth”
microMIKE-roeGreek: “small”
nanoNAN-ohGreek: “dwarf”
picoPEEK-ohSpanish: “tiny bit”
femtoFEM-toeDano-Norwegian: “fifteen”
attoAT-toeDano-Norwegian: “eighteen”
zeptoZEP-toeLatin: “seven” [(103)-7]
yoctoYOCK-toeLatin: “eight” [(103)-8]

These tables were provided by David Bernklau, Certified Metrication Specialist (CMS), The first table is an expanded version of Table 2 published in Practical Guide to the International System of Units by Dennis Brownridge.

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Updated: 2014-08-05