# SI Prefixes or Metric prefixes

### In this section

In order to make many of the SI units more easy to manage a system of SI prefixes, often called metric prefixes is used.

As the name indicates, the SI prefix, or metric prefix precedes the associated symbol to form a decimal multiple or sub-multiple.

These prefixes are particularly useful and reduce the number of zeros for a given quantity, making them easier to read and manage.

These SI prefixes or metric prefixes are in widespread use in all areas of life.

## Table of SI prefixes

Factor Prefix Symbol Decimal
1024 yotta Y 1 000 000 000 000 000 000 000 000
1021 zetta Z 1 000 000 000 000 000 000 000
1018 exa E 1 000 000 000 000 000 000
1015 peta P 1 000 000 000 000 000
1012 tera T 1 000 000 000 000
109 giga G 1 000 000 000
106 mega M 1 000 000
103 kilo k 1 000
102 hecto h 100
101 deca da 10
10-1 deci d 0.1
10-2 centi c 0.01
10-3 milli- m 0.001
10-6 micro µ 0.000 001
10-9 nano n 0.000 000 001
10-12 pico p 0.000 000 000 001
10-15 femto f 0.000 000 000 000 001
10-18 atto a 0.000 000 000 000 000 001
10-21 zepto z 0.000 000 000 000 000 000 001
10-24 yocto y 0.000 000 000 000 000 000 000 001

## Examples of SI prefixes

In total there are twenty prefixes that have been officially adopted to be used with the various units of measure. They are widely used and are easy to add to the basic units. A few examples are given below:

• 1 kilowatt = 1000 watts
• 1 kilogram = 1000 grams
• 1 kilovolt = 1000 volts
• etc ... etc ...

Along with these the abbreviations or symbols can also be used. For example kV for kilovolts; kW for kilowatts, and km for kilometre. The other symbols or abbreviations can be used in exactly the same manner. However it is necessary to ensure that the case is correct. Many times frequencies of 10 mHz have been seen when what is really meant is 10 MHz!

SI prefixes are internationally recognized and have been in use for many years. In fact many of them pre-date SI itself and have been used since the metric system was first introduced - hence the name of metric prefixes that is often used for them. In addition to this many of these SI prefixes or metric prefixes are used with many non-SI units or even non-metric units: for example: milligauss (mG), microinch(µin), etc....

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