A metric prefix is a word which is added to the beginning of a base unit to show a multiple of that unit. All metric prefixes are powers of $10.$ Metric prefixes can be considered as an alternative to the scientific notation. For example, $7.3\times 10^3$ grams can be written as $7.3$ kilograms since the prefix kilo means $10^3.$ Each metric prefix has a unique symbol that can precede any unit symbol.

Metric Prefixes Greater Than $1$
Prefix	Symbol	Power
peta	P	$10^{15}$
tera	T	$10^{12}$
giga	G	$10^9$
mega	M	$10^6$
kilo	k	$10^3$
hecto	h	$10^2$
deca	da	$10^1$

Notice that the symbols for the prefixes greater than $1$ are uppercase letters, except for kilo, hecto, and deca. There is no prefix used for $10^0=1.$ The metric prefixes less than $1$ are shown in the following table.

Metric Prefixes Less Than $1$
Prefix	Symbol	Power
deci	d	$10^{\text{-}1}$
centi	c	$10^{\text{-}2}$
milli	m	$10^{\text{-}3}$
micro	μ	$10^{\text{-}6}$
nano	n	$10^{\text{-}9}$
pico	p	$10^{\text{-}12}$
femto	f	$10^{\text{-}15}$

Note that the prefix names cannot be used together. Another important note is that the International System of Units base unit of mass, kilogram, already contains a prefix. Since multiple prefixes are not allowed, the prefix names shown in the tables are used with the unit gram (g).