When a numerical
quantity is either very large or very small, the units used to define its size
may be modified using a prefix. Some of the prefixes used in the SI system are
shown in table. Each represent a multiple or submultiples which, if
applied successively, moves the decimal point to every third place. Except for
some volume and area measurement, the use of these prefixes is to be avoided in
sciences and engineering.
Multiple
|
Exponential Form
|
Prefix
|
SI Symbol
|
1 000 000 000
|
109
|
giga
|
G
|
1 000 000
|
106
|
mega
|
M
|
1 000
|
103
|
kilo
|
K
|
Submultiple
|
|||
0.001
|
10-3
|
milli
|
M
|
0.000 001
|
10-6
|
micro
|
µ
|
0.000 000 001
|
10-9
|
nano
|
N
|
Rules for Use
The following rules are
given for the proper use of various SI symbols:
- A symbol is never written with a plural “s”, since it may be confused with the unit for second (s).
- Symbols are always written in lowercase letters, with the following exceptions: symbols for the two largest prefixes, giga and mega, are capitalized as G and M, respectively, and symbols named after an individual are also capitalized.
- Quantities defined by several units which are multiple of one another are separated by a dot to avoid confusion with prefix notation, as indicated by N = 1 kg.m.s-2. Also, m.s (meter-second), whereas ms (milli-second).
- The exponential power represented for a unit having a prefix refers to both the unit and its prefix.
- With the exception of the base unit the kilogram, in general avoid the use of a prefix in the denominator of composite function.
