Numerical Prefixes
Milli is a common prefix used in electronics and car audio. It refers to 1/1000 of something. For example, one millivolt is .001 volt or 1/1000 of one volt. Micro refers to one millionth of something. It is commonly used in stating the value of capacitors. For example, a capacitor with a value of one microfarad has one millionth of the capacitance of a one farad capacitor.
In the following table, I'll use the unit 'watts' to show how the prefixes affect the nomenclature.
Common Prefixes Used in Electronics 
1 terawatt  =  1,000,000,000,000 Watts 
1 gigawatt  =  1,000,000,000 Watts 
1 megawatt  =  1,000,000 Watts 
1 kilowatt  =  1,000 Watts 
1 milliwatt  =  0.001 Watts 
1 microwatt  =  0.000001 Watts 
1 nanowatt  =  0.000000001 Watts 
1 picowatt  =  0.000000000001 Watts 
1 femtowatt  =  0.000000000000001 Watts 

In the following converter:

You can enter up to a 5 digit number

Enter a number on the left and click the prefix of that number (x1 for whole numbers). Then click the prefix that you want to convert it to on the right.

Start out with 'x1' on the left if you don't fully understand how the conversion works. It will be less confusing.

If you enter '12' and 'x1' on the left then click micro on the right, it will show you that the whole number 12 is equal to 12,000,000 micro somethings.

If you click '15' and 'micro' on the left then click 'x1' on the right it will tell you that 15 micro (microfarads for example) is equal to 0.000015 (farads).

To see how many amps 250 milliamps is equal to, enter 250 on the left, click milli on the left and then 'x1' on the right.
Dimensional Analysis:
When trying to convert a value with one type of unit (such as 1 cubic foot) to another type of units (such as liters), you can use a tool known as dimensional analysis. It's a pretty simple method that reduces errors when making conversions.
As you alread know, you can multiply or divide anything by 'one' and its value doesn't change. You should also know that you can divide a number by itself (or an equivalent value) and the result is equal to one. A volume of 1ft³ is equal to ~28.3 liters. This means that 1ft³/28.3 liters is equal to '1'. If we know a woofer needs 45 liters but you want to know what that is in ft³, you can use dimensional analysis to make the calculations.
?ft³ =

45 liters


1


* 
1 ft³


28.3 liters


In the following fraction you can see how the 'same units' cancel out. This leaves only the values (numbers) and a single type of unit (ft³) to deal with. You then simply multiply straight across to get the final value. To simplify, you'd divide 45 by 28.3. 45 liters is equal to 1.59ft³.
Volume =

45 liters


1


* 
1 ft³


28.3 liters


Volume =

1.59ft³


1


This will work for any number of conversions. If we don't know a direct conversion we can use any number of equivalent values to get to the final value. If we wanted to know how many gallons it would take to fill 1ft³ (and didn't know a direct conversion), we could go the 'long way 'round' to get the answer.
1 gallon


4 quarts


* 
1.057 quarts


1 liter


* 
28.3 liters


1 ft³


Cancel out like terms (units).
1 gallon


4 quarts


* 
1.057 quarts


1 liter


* 
28.3 liters


1 ft³


Multiply straight across.
1 gallon


4


* 
1.057


1


* 
28.3


1 ft³


You can see that you'd have 29.91 gallons per 4ft³
29.91 gallon


4 ft³


OR...
7.48 gallon


1 ft³


To see it in a more traditional form, we can multiply both sides by 1ft³/1 (multiplying both sides of the equation by the same number will not change the value of the answer).
1ft³


1


= 
7.48 gallons


1


