The Metric System

The Metric System, it’s prefixes and how to convert between them.

A measurement made in the metric system, also known as SI (International System of Units) requires three parts.

  • Numeric Value
  • Prefix
  • Unit of Measure

Numeric Value

The count of how many units are being referenced. This number will be a function of the prefix.


Because using all the zeros in very large or very small numbers can be very cumbersome, the metric system utilizes the prefix to apply a numeric multiplier to a measurement so that you can more easily work with any number of any scale, large or small. Rather than trying to remember a specific multiplier by the number of zeros in it, that multiplier can be referenced by the prefix assigned to it.

Refer to the following chart to find value of a prefix.

Prefix Symbol Base 10 Decimal
quetta Q 1030 1,000,000,000,000,000,000,000,000,000,000
ronna R 1027 1,000,000,000,000,000,000,000,000,000
yotta Y 1024 1,000,000,000,000,000,000,000,000
zetta Z 1021 1,000,000,000,000,000,000,000
exa E 1018 1,000,000,000,000,000,000
peta P 1015 1,000,000,000,000,000
tera T 1012 1,000,000,000,000
giga G 109 1,000,000,000
mega M 106 1,000,000
kilo k 103 1,000
hecto h 102 100
deca da 101 10
100 1
deci d 10−1 0.1
centi c 10−2 0.01
milli m 10−3 0.001
micro μ 10−6 0.000001
nano n 10−9 0.000000001
pico p 10−12 0.000000000001
femto f 10−15 0.000000000000001
atto a 10−18 0.000000000000000001
zepto z 10−21 0.000000000000000000001
yocto y 10−24 0.000000000000000000000001
ronto r 10−27 0.000000000000000000000000001

Notice how in the Base10 column we have 10 to a specific power. That is the number of positions the decimal has to move from Base 100. Also note, it does jump and not all positions have names. For example; micro to pico, even though they one proceeds the other, there is a gap of 3 decimal places.

“µ” , What is it and why?

The Metric System uses capital letters for prefixes that represent multipliers larger than 1,000,000 and lower case for those smaller. It also uses one letter prefixes which means that mega and milli had already taken the “M’s” It was decided that the Greek letter mu (µ) would be used to represent micro.

Most keyboards do not have a “µ” key. This means that using it can be difficult and why you will see it represented as regular “u” sometimes.

how to enter µ on your keyboard

For all keyboard layouts

  • On Microsoft Windows systems,

    • arbitrary Unicode codepoints can be entered in hexadecimal as: Alt+0181; note that a leading “0” is required, or
  • On Linux systems,

    • arbitrary Unicode codepoints can be entered in hexadecimal as: Ctrl+⇧ Shift+u b5space, or

For QWERTY keyboard layouts

  • On Linux systems,
    • code-point U+00b5 can be entered as right-alt+m (provided the right alt key is configured to act as AltGr).
  • On MacOS systems, code-point U+00b5 can be entered as either ⌥ Opt+m or ⌥ Opt+Y.
Some information derived from the following web page:
Metric prefix - Wikipedia.


International System of Units

What it measures Name of Unit Symbol
second second s
length meter m
mass kilogram kg
electric current ampere A
thermodynamic temperature kelvin K
luminous intesity candela cd
amount of substance mole mol

The National Institute of Standards and Technology (NIST) has this graphic to explain units in greater detail.

Click here to visit the NIST Metric and SI Webpage

Putting it all together


Numeric Value Prefix Unit of Measure Expression
10 kilo meter 10km
0.1 micro ampere 0.1µA


Sometimes a number will not be easy to write or look correct unless it is converted up or down the scale.


Starting Value Number of positions to move. Ending Value
1km 3 1000m
0.1µA 6 100,000pA