• Used to indicate multiples or fractions of a unit
• Based on the decimal system – represent multiples of 10
• Standardised for use in the international system of units
• Units still considered to be SI units when given a prefix
Prefix Name
Prefix Symbol
Base 10
English Word
yotta
Y
1024
septillion
zetta
Z
1021
sextillion
exa
E
1018
quintillion
peta
P
1015
tera
T
1012
trillion
giga
G
109
billion
mega
M
106
million
kilo
k
103
thousand
hecto
h
102
hundred
deca
da
101
ten
100
one
deci
d
10−1
tenth
centi
c
10−2
hundredth
milli
m
10−3
thousandth
micro
μ
10−6
millionth
nano
n
10−9
billionth
pico
p
10−12
trillionth
femto
f
10−15