Mega is a unit prefix in metric systems of units denoting a factor of one million (10^{6} 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, romanized: mégas, lit. 'great'.^{[1]}
When units occur in exponentiation, such as in square and cubic forms, any multiplesprefix is considered part of the unit, and thus included in the exponentiation.
In some fields of computing, mega may sometimes denote 1,048,576 (2^{20}) of information units, for example, a megabyte, a megaword, but denotes 1000000 (10^{6}) units of other quantities, for example, transfer rates: 1megabit/s = 1000000bit/s. The prefix mebi has been suggested as a prefix for 2^{20} to avoid ambiguity.
Prefix  Base 10  Decimal  Adoption ^{[nb 1]}  

Name  Symbol  
quetta  Q  10^{30}  1000000000000000000000000000000  2022 
ronna  R  10^{27}  1000000000000000000000000000  2022 
yotta  Y  10^{24}  1000000000000000000000000  1991 
zetta  Z  10^{21}  1000000000000000000000  1991 
exa  E  10^{18}  1000000000000000000  1975 
peta  P  10^{15}  1000000000000000  1975 
tera  T  10^{12}  1000000000000  1960 
giga  G  10^{9}  1000000000  1960 
mega  M  10^{6}  1000000  1873 
kilo  k  10^{3}  1000  1795 
hecto  h  10^{2}  100  1795 
deca  da  10^{1}  10  1795 
10^{0}  1  —  
deci  d  10^{−1}  0.1  1795 
centi  c  10^{−2}  0.01  1795 
milli  m  10^{−3}  0.001  1795 
micro  μ  10^{−6}  0.000001  1873 
nano  n  10^{−9}  0.000000001  1960 
pico  p  10^{−12}  0.000000000001  1960 
femto  f  10^{−15}  0.000000000000001  1964 
atto  a  10^{−18}  0.000000000000000001  1964 
zepto  z  10^{−21}  0.000000000000000000001  1991 
yocto  y  10^{−24}  0.000000000000000000000001  1991 
ronto  r  10^{−27}  0.000000000000000000000000001  2022 
quecto  q  10^{−30}  0.000000000000000000000000000001  2022 
