Exa-

This article is about the SI prefix. For other uses, see Exa (disambiguation).

Exa is a decimal unit prefix in the metric system denoting 10¹⁸ or 1000000000000000000. It was added as an SI prefix to the International System of Units (SI) in 1975, and has the unit symbol E.

Exa comes from the Ancient Greek ἕξ, used as a prefix ἑξά-, meaning six (like hexa-), because it is equal to 1000⁶.

Examples:

• The total storage needed by Google Mail as of April 2012, ignoring backups and compression, is more than an exabyte (10,240 megabytes of storage per user multiplied by an estimated 260 million users).
• 1 EeV = 10¹⁸ electronvolts = 0.1602 joule
• 1 exasecond is approximately 32 billion years
• 1 exametre is approximately 110 light years
• 0.43 Es ≈ the approximate age of the Universe
• 1.6 Em—172 ± 12.5 light years—Diameter of Omega Centauri (one of the largest known globular clusters, perhaps containing over a million stars)

SI prefixes

Prefix 1000m 10n Decimal English word Adoption Name Symbol Short scale Long scale yotta Y  10008  1024 1000000000000000000000000  septillion  quadrillion 1991 zetta Z  10007  1021 1000000000000000000000  sextillion  thousand trillion or trilliard 1991 exa E  10006  1018 1000000000000000000  quintillion  trillion 1975 peta P  10005  1015 1000000000000000  quadrillion  thousand billion or billiard 1975 tera T  10004  1012 1000000000000  trillion  billion 1960 giga G  10003  109 1000000000  billion  thousand million or milliard 1960 mega M  10002  106 1000000             million 1960 (1873) kilo k  10001  103 1000             thousand 1960 (1795) hecto h  10002/3  102 100             hundred 1960 (1795) deca da  10001/3  101 10             ten 1960 (1795)  10000  100 1             one – deci d  1000−1/3  10−1 0.1             tenth 1960 (1795) centi c  1000−2/3   10−2 0.01             hundredth 1960 (1795) milli m  1000−1  10−3 0.001             thousandth 1960 (1795) micro μ  1000−2  10−6 0.000001             millionth 1960 (1873) nano n  1000−3  10−9 0.000000001  billionth  thousand millionth 1960 pico p  1000−4  10−12 0.000000000001  trillionth  billionth 1960 femto f  1000−5  10−15 0.000000000000001  quadrillionth  thousand billionth 1964 atto a  1000−6  10−18 0.000000000000000001  quintillionth  trillionth 1964 zepto z  1000−7  10−21 0.000000000000000000001  sextillionth  thousand trillionth 1991 yocto y  1000−8  10−24  0.000000000000000000000001  septillionth  quadrillionth  1991

See also

• 1 exametre
• Exabyte
• Exasecond
• Orders of magnitude (numbers)
• Metric prefix
• Binary prefix

External links

• BIPM website
• Exa Corporation
• Exa Proxy Testhe:תחיליות במערכת היחידות הבינלאומית#אקסה