Mega-
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Mega-

Mega is a unit prefix in metric systems of units denoting a factor of one million (106 or 1000000). It has the unit symbol M. It was confirmed for use in the International System of Units (SI) in 1960. Mega comes from Ancient Greek: , romanizedmégas, lit.'great'.[1]

## Exponentiation

When units occur in exponentiation, such as in square and cubic forms, any multiples-prefix is considered part of the unit, and thus included in the exponentiation.

• 1 Mm2 means one square megametre or the size of a square of 1000000m by 1000000m or 1012m2, and not 1000000square metres (106 m2).
• 1 Mm3 means one cubic megametre or the size of a cube of 1000000m by 1000000m by 1000000m or 1018 m3, and not 1000000cubic metres (106 m3)

## Computing

In some fields of computing, mega may sometimes denote 1,048,576 (220) of information units, for example, a megabyte, a megaword, but denotes 1000000 (106) units of other quantities, for example, transfer rates: 1megabit/s = 1000000bit/s. The prefix mebi- has been suggested as a prefix for 220 to avoid ambiguity.

SI prefixes
Prefix Base 10 Decimal English word Adoption[nb 1] Etymology
Name Symbol Short scale Long scale Language Derived word
yotta Y  1024 1000000000000000000000000  septillion  quadrillion 1991 Greek eight[nb 2]
zetta Z  1021 1000000000000000000000  sextillion  trilliard 1991 Latin seven[nb 2]
exa E  1018 1000000000000000000  quintillion  trillion 1975 Greek six
peta P  1015 1000000000000000  quadrillion  billiard 1975 Greek five[nb 2]
tera T  1012 1000000000000  trillion  billion 1960 Greek four[nb 2], monster
giga G  109 1000000000  billion  milliard 1960 Greek giant
mega M  106 1000000  million 1873 Greek great
kilo k  103 1000  thousand 1795 Greek thousand
hecto h  102 100  hundred 1795 Greek hundred
deca da  101 10  ten 1795 Greek ten
100 1  one -
deci d  10-1 0.1  tenth 1795 Latin ten
centi c  10-2 0.01  hundredth 1795 Latin hundred
milli m  10-3 0.001  thousandth 1795 Latin thousand
micro ?  10-6 0.000001  millionth 1873 Greek small
nano n  10-9 0.000000001  billionth  milliardth 1960 Greek dwarf
pico p  10-12 0.000000000001  trillionth  billionth 1960 Spanish peak
femto f  10-15 0.000000000000001  quadrillionth  billiardth 1964 Danish fifteen, Fermi[nb 3]
atto a  10-18 0.000000000000000001  quintillionth  trillionth 1964 Danish eighteen
zepto z  10-21 0.000000000000000000001  sextillionth  trilliardth 1991 Latin seven[nb 2]
yocto y  10-24  0.000000000000000000000001  septillionth  quadrillionth 1991 Greek eight[nb 2]
1. ^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.
2. Part of the beginning of the prefix was modified from the word it was derived from, ex: "peta" (prefix) vs "penta" (derived word).
3. ^ The fermi was introduced earlier with the same symbol "fm", in which then the "f" became a prefix. The Danish word is used since it is vaguely spelled similar to fermi.

## References

1. ^ "Oxford English Dictionary (OED Online)". www.oed.com (3rd ed.). Oxford University Press. June 2001. Retrieved . Origin: A borrowing from Greek. Etymon: Greek ?-. ... Forming scientific and technical terms with the sense 'very large', 'comparatively large', or (esp. in Pathol.) 'abnormally large', often having correlatives beginning micro-, and sometimes also synonyms beginning macro-.