5.1.6 Working with a Common Unit
When you are using measurements in calculations, you often need to convert all the measurements into the same units before you start the calculation. This would be the case for example if you wanted to calculate the perimeter of something and you had some of the measurements in centimeters and others in meters. It does not make sense to add centimeters and meters so you would need to convert.
For example, suppose you wanted to convert 2.3 meters (m) into centimeters (cm). We know that there are 100 cm in 1 m. So, to convert a measurement in m into cm, we need to multiply by 100. So, .
You can see how to convert from one unit of length to another in the SI, in the diagram below. Notice that to convert from a big unit to a smaller unit, you multiply. This makes sense—you will need a lot more of the smaller units. On the other hand, to convert a measurement in a small unit to a bigger unit, you divide. The same logic works when converting in other measurement systems and it always worth pausing and asking yourself if you final answer should be bigger or smaller than the original value you have.