# 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: μέγας, 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 1048576 (220) information units, for example, a megabyte, a megaword, but denotes 1000000 (106) units of other quantities, for example, transfer rates: 1megabit/s = 1000000bit/s. In the case of 3½-inch floppy disks, sizes were given in megabytes of 1000KB or 1024000 bits.[2] The prefix mebi- has been suggested as a prefix for 220 to avoid ambiguity.

Prefix Base 10 Decimal Adoption
[nb 1]
Name Symbol
quetta Q 1030 1000000000000000000000000000000 2022[3]
ronna R 1027 1000000000000000000000000000
yotta Y 1024 1000000000000000000000000 1991
zetta Z 1021 1000000000000000000000
exa E 1018 1000000000000000000 1975[4]
peta P 1015 1000000000000000
tera T 1012 1000000000000 1960
giga G 109 1000000000
mega M 106 1000000 1873
kilo k 103 1000 1795
hecto h 102 100
deca da 101 10
100 1
deci d 10−1 0.1 1795
centi c 10−2 0.01
milli m 10−3 0.001
micro μ 10−6 0.000001 1873
nano n 10−9 0.000000001 1960
pico p 10−12 0.000000000001
femto f 10−15 0.000000000000001 1964
atto a 10−18 0.000000000000000001
zepto z 10−21 0.000000000000000000001 1991
yocto y 10−24 0.000000000000000000000001
ronto r 10−27 0.000000000000000000000000001 2022[3]
quecto q 10−30 0.000000000000000000000000000001
Notes
1. ^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.