How to Calculate a Ratio

Step-by-step

1. Identify the quantities you want to compare.
2. Write the values in the same order as the comparison in your question.
3. Check that both values use compatible units.
4. Simplify the ratio by dividing each value by their greatest common divisor when applicable.
5. Use the result to check the comparison or calculate an equivalent ratio.

How ratio simplification works

A ratio such as 12:8 can be simplified by dividing both numbers by 4, giving 3:2. Keep the order of the quantities intact because 3:2 and 2:3 describe different relationships.

Avoid mixing units

Convert values to compatible units before comparing them. For example, compare centimetres with centimetres rather than mixing centimetres and metres without conversion.