Solve a proportion such as A is to B as C is to what, and simplify any ratio to its lowest terms.
D (so that A : B = C : D)
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| A : B in simplest form | – |
| Scale factor (C ÷ A) | – |
| A ÷ B as a decimal | – |
How it works
Two ratios are equal when A ÷ B = C ÷ D. Solving for the unknown gives D = B × C ÷ A. To simplify a ratio, divide both parts by their greatest common divisor.
Example
If 3 : 4 = 9 : D, then D = 4 × 9 ÷ 3 = 12. The ratio 3 : 4 is already in simplest form.
Frequently asked questions
What is a ratio?
A comparison of two quantities, written A : B.
How do I scale a recipe with a ratio?
Find the scale factor, the new amount divided by the old, and multiply every ingredient by it.
Can I use decimals?
Yes. The simplified ratio is calculated to three decimal places.
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This calculator is for general guidance.