A unit tells you what a number measures. Before converting, make sure you understand both the starting unit and the unit you want at the end. A correct number with the wrong unit can still be misleading.
Use conversion factors
Many conversions use a fixed factor. For example, one metre equals 100 centimetres, so metres can be changed to centimetres by multiplying by 100. Reverse the operation to go back.
Temperature is different
Celsius and Fahrenheit do not share the same zero point, so temperature conversion needs both multiplication and addition or subtraction. Do not treat it like a simple length conversion.
Keep precision sensible
Use enough decimal places for the task, but do not create false precision. A rough travel measurement does not need the same precision as a laboratory measurement.
Check the result
Ask whether the direction makes sense. Converting metres to centimetres should give a larger number; converting grams to kilograms should give a smaller one.
Quick questions
Should I round before converting?
Usually round at the end so that small early rounding errors do not grow.
Can I mix metric and imperial values?
Yes, but convert one value first so the calculation uses a single system.
Last reviewed: 5 September 2026. If you spot an error, use our feedback page.