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.
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  10^{30}  1,000,000,000,000,000,000,000,000,000,000 
ronna  R  10^{27}  1,000,000,000,000,000,000,000,000,000 
yotta  Y  10^{24}  1,000,000,000,000,000,000,000,000 
zetta  Z  10^{21}  1,000,000,000,000,000,000,000 
exa  E  10^{18}  1,000,000,000,000,000,000 
peta  P  10^{15}  1,000,000,000,000,000 
tera  T  10^{12}  1,000,000,000,000 
giga  G  10^{9}  1,000,000,000 
mega  M  10^{6}  1,000,000 
kilo  k  10^{3}  1,000 
hecto  h  10^{2}  100 
deca  da  10^{1}  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,
 codepoint U+00b5 can be entered as rightalt+m (provided the right alt key is configured to act as
AltGr
).
 codepoint U+00b5 can be entered as rightalt+m (provided the right alt key is configured to act as
 On MacOS systems, codepoint U+00b5 can be entered as either ⌥ Opt+m or ⌥ Opt+Y.
Some information derived from the following web page:
Metric prefix  Wikipedia.
Units
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
Examples:
Numeric Value  Prefix  Unit of Measure  Expression 

10  kilo  meter  10km 
0.1  micro  ampere  0.1µA 
Conversions:
Sometimes a number will not be easy to write or look correct unless it is converted up or down the scale.
Examples:
Starting Value  Number of positions to move.  Ending Value 

1km  3  1000m 
0.1µA  6  100,000pA 