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Ratio Calculator

Enter the two parts of a ratio to simplify it. Add a new value for the first part to scale the second part to match.

The first number in the ratio A : B. Decimals are allowed.

The second number in the ratio.

Optional. Enter the value A should become, and you get the matching B.

This result is an estimate only. Double-check important figures before relying on them.

How it is calculated

  • Decimals are scaled to whole numbers by multiplying both parts by 10, 100 and so on
  • Both parts are divided by their greatest common factor
  • A ÷ B = the first part divided by the second
  • Share of A = A ÷ (A + B) × 100
  • New B = new A × B ÷ A

To find the greatest common factor yourself, use the GCF calculator. For percentages, use the percentage calculator.

Worked example

The ratio 15 : 25:

  • Greatest common factor: 5
  • Simplified ratio: 15 ÷ 5 : 25 ÷ 5 = 3 : 5
  • A as a share of the total: 15 ÷ 40 = 37.5%
  • If A becomes 12, B = 12 × 25 ÷ 15 = 20

Why your number may differ

Decimals with more than six places are not accepted, because they cannot be turned into whole numbers reliably. A ratio with a zero part is shown as 0 : 1 or 1 : 0.

Frequently asked questions

How do I simplify a ratio?

Divide both parts by their greatest common factor. For 15 : 25 the greatest common factor is 5, so the ratio is 3 : 5.

How do I scale a ratio?

Keep A ÷ B the same. If 15 : 25 becomes 12 : x, then x = 12 × 25 ÷ 15 = 20.

Can a ratio have decimals?

Yes. The calculator first multiplies both parts by a power of 10 to remove the decimals, then simplifies.

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