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Ratio Calculator

Solve a missing value in A:B = C:D, simplify a ratio to its lowest terms, or split an amount in a given ratio. Free ratio and proportion calculator.

D
20
Ratio
3 : 4 = 15 : 20

Ratios and proportions

A ratio compares two quantities. Two ratios are in proportion when they're equal, so A:B = C:D means A × D = B × C. To solve 3:4 = 15:D, cross-multiply: D = 4 × 15 ÷ 3 = 20. Simplifying divides both sides by their greatest common divisor, so 1.5:2.25 becomes 2:3. Splitting an amount shares it out in a ratio: 700 split 3:4 is 300 and 400. Use it for recipes, scale drawings, mixing paint or sharing costs.

How to use it

  1. 1

    Pick a calculation

    Solve a proportion, simplify a ratio or split an amount.

  2. 2

    Enter the numbers

    Leave the unknown value empty when solving.

  3. 3

    Read the answer

    The missing value, the simplest form or each share.

Frequently asked questions

How do I solve a proportion?

Cross-multiply and divide: if A:B = C:D, then D = B × C ÷ A.

How do I simplify a ratio?

Divide both numbers by their greatest common divisor. 12:18 ÷ 6 = 2:3.

How do I divide an amount in a ratio?

Add the parts, divide the amount by the total, then multiply by each part. 700 in 3:4 is 700 ÷ 7 = 100, so 300 and 400.

Is anything stored?

No. The calculation runs in your browser.

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