To convert between units you have and units you need it's all about placement.
First, make sure you are converting between the same unit type.
For example, inches and feet, or inches and centimeters are units of length. It is not possible to convert between inches and grams because grams are a unit of weight.
Next, you'll need a conversion factor. The conversion factor is a ratio of the two units. This can also be referred to as the "equivalent value". Because the numerator is equal to the denominator, the fraction is technically equal to one.
For example, 12 inches = 1 foot. This can also be written as a fraction:
The conversation factor fraction is handy because it can be written in whichever configuration you need.
The most important thing to remember when you are converting is to multiply by what you need and divide by what you have. When written out, you should create a criss cross when eliminating units.
The easiest way to perform a unit conversion is by using fractions and writing out the units. This way you can see if your “criss-crosses” are correct.
Let's do a conversion!
This same method can be used for any type of unit conversion such as Energy, Weight, Amount, Temperature, Time, Electric Current, Luminous Intensity, and Mass.
Check out this post for an energy conversion (What are CCf, Mcf, Btu, and therms? How do I convert natural gas prices in dollars per Ccf or Mcf to dollars per Btu or therm?)