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From Wikipedia, the free encyclopedia

Zetta (symbol Z) is a prefix in the International System of Units (SI) denoting a factor of 1021 or 1000000000000000000000.

Added to the SI in 1991, it is derived from the French prefix septo, meaning seven, because it is equal to 10007.[1]

A prefix of the same value, hepta, was informally introduced a few years before the promulgation of zetta. It was formed from the Greek ἑπτά, (hepta), also meaning seven. Hepta never received official sanction and is now obsolete.

SI prefixes
1000m 10n Prefix Symbol Since[1] Short scale Long scale Decimal
10008 1024 yotta Y 1991 Septillion Quadrillion 1000000000000000000000000
10007 1021 zetta Z 1991 Sextillion Trilliard 1000000000000000000000
10006 1018 exa E 1975 Quintillion Trillion 1000000000000000000
10005 1015 peta P 1975 Quadrillion Billiard 1000000000000000
10004 1012 tera T 1960 Trillion Billion 1000000000000
10003 109 giga G 1960 Billion Milliard 1000000000
10002 106 mega M 1960 Million 1000000
10001 103 kilo k 1795 Thousand 1000
100023 102 hecto h 1795 Hundred 100
100013 101 deca da 1795 Ten 10
10000 100 (none) (none) NA One 1
100013 10−1 deci d 1795 Tenth 0.1
100023 10−2 centi c 1795 Hundredth 0.01
1000−1 10−3 milli m 1795 Thousandth 0.001
1000−2 10−6 micro µ 1960[2] Millionth 0.000001
1000−3 10−9 nano n 1960 Billionth Milliardth 0.000000001
1000−4 10−12 pico p 1960 Trillionth Billionth 0.000000000001
1000−5 10−15 femto f 1964 Quadrillionth Billiardth 0.000000000000001
1000−6 10−18 atto a 1964 Quintillionth Trillionth 0.000000000000000001
1000−7 10−21 zepto z 1991 Sextillionth Trilliardth 0.000000000000000000001
1000−8 10−24 yocto y 1991 Septillionth Quadrillionth 0.000000000000000000000001
  1. The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM.
  2. The 1948 recognition of the micron by the CGPM was abrogated in 1967.


  1. ^ "Resolution 4 of the 19th CGPM (Conférence Générale des Poids et Mesures)". BIPM (Bureau International des Poids et Mesures). Retrieved 2009-05-16. "The names zepto and zetta are derived from septo suggesting the number seven (the seventh power of 103) and the letter "z" is substituted for the letter "s" to avoid the duplicate use of the letter "s" as a symbol."  

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Up to date as of January 14, 2010
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Definition from Wiktionary, a free dictionary

See also Zetta-




From Ancient Greek ἑπτά (hepta), for the seventh order of 103. The consonants pt are reduced to tt as in Italian, by analogy with peta-; the letter z was added, as a start to running through the alphabet backwards.


SI prefix
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Next: yotta-


  1. In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by 1021. Symbol: Z




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