
SI prefixes
The 20 SI prefixes used to form decimal multiples and submultiples of SI units are given in Table 5.
Table 5. SI prefixes

Factor 
Name 
Symbol 
10^{24} 
yotta 
Y 
10^{21} 
zetta 
Z 
10^{18} 
exa 
E 
10^{15} 
peta 
P 
10^{12} 
tera 
T 
10^{9} 
giga 
G 
10^{6} 
mega 
M 
10^{3} 
kilo 
k 
10^{2} 
hecto 
h 
10^{1} 
deka 
da 


Factor
 Name
 Symbol

10^{1} 
deci 
d 
10^{2} 
centi 
c 
10^{3} 
milli 
m 
10^{6} 
micro 
µ 
10^{9} 
nano 
n 
10^{12} 
pico 
p 
10^{15} 
femto 
f 
10^{18} 
atto 
a 
10^{21} 
zepto 
z 
10^{24} 
yocto 
y 


It is important to note that the kilogram is the only SI unit with a prefix
as part of its name and symbol. Because multiple prefixes may not be used,
in the case of the kilogram the prefix names of Table 5 are used
with the unit name "gram" and the prefix symbols are used with
the unit symbol "g." With this exception, any SI prefix may
be used with any SI unit, including the degree Celsius and its symbol
°C.
Example 1: 
10^{6} kg = 1 mg (one milligram), but not
10^{6} kg = 1 µkg (one microkilogram) 
Example 2: 
Consider the earlier example of the height of the Washington Monument.
We may write h_{W} = 169 000 mm
= 16 900 cm = 169 m = 0.169 km using the millimeter (SI prefix
milli, symbol m), centimeter (SI prefix centi, symbol c), or kilometer
(SI prefix kilo, symbol k). 
Because the SI prefixes strictly represent powers of 10, they should not be used
to represent powers of 2. Thus, one kilobit, or 1 kbit, is 1000 bit and
not 2^{10} bit = 1024 bit. To alleviate this
ambiguity, prefixes for binary multiples have
been adopted by the International Electrotechnical Commission (IEC) for
use in information technology.
Continue to Units outside the SI
