justyourcalculatorRatio Calculator
Fill in three parts of a proportion, or simplify and scale any ratio.
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Ratio Calculator
Solve A:B = C:D, scale and simplify ratios
Leave one box empty.
D
16
3 : 4 = 12 : 16
How it was calculated
- A / B = C / D, so A × D = B × C (cross-multiply)
- D = B × C / A = 4 × 12 / 3
- D = 16
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How the ratio calculator works
A ratio compares two quantities, written A : B. Two ratios are equal (a proportion) when A / B = C / D, which is the same as A × D = B × C. Cross-multiplying and dividing gives any one missing value.
To simplify a ratio, divide both parts by their greatest common factor: 24 : 36 becomes 2 : 3. Decimals are first scaled to whole numbers. Scaling multiplies or divides both parts by the same factor, which is how recipes and maps change size without changing proportions.
Using and checking your result
Published by JustYourCalculator. Check the units and assumptions above, and compare a known example before relying on the output. Calculations use browser arithmetic and may round displayed values.
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