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SnapRatios

Ratio & proportion tools

How to Calculate a Ratio

Four steps, one worked example, no detours.

The four steps

Method

  1. Identify the two quantities you are comparing and the order they belong in.
  2. Put them in the same unit — 500 g and 1 kg is 500:1000, not 500:1.
  3. Write them as A:B.
  4. Divide both parts by their greatest common divisor to simplify.

Worked example: 12 and 18

Twelve and eighteen are already in the same unit, so the ratio is 12:18. Their greatest common divisor is 6, so dividing both parts gives 2:3. There are five total parts, meaning the first quantity is 40% of the whole and the second is 60%.

Checking your answer

Multiply the simplified ratio back up: 2 × 6 = 12 and 3 × 6 = 18. If both parts return to the original numbers with the same multiplier, the ratio is correct.