Ratio Calculator
Solve proportions and simplify ratios.
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About the Ratio Calculator
Solve ratios and proportions free — enter three values in A : B = C : D and leave one box blank, and the calculator solves for the missing number using cross-multiplication. It also simplifies your A : B ratio to its lowest terms. Handy for scaling recipes, mixing paint or chemicals, converting map scales, resizing images, and any “if this, then how much of that?” problem.
How to use the Ratio Calculator
- 01Enter three of the four values (A : B = C : D).
- 02Leave the unknown box blank.
- 03Read the solved value and the simplified ratio.
Frequently asked questions
How does it solve a proportion?
It cross-multiplies — for A : B = C : D, the missing value is found so that A × D equals B × C.
Can it simplify a ratio?
Yes — enter A and B and it reduces the ratio to its lowest whole-number terms using the greatest common divisor.
What can I use ratios for?
Scaling recipes, mixing solutions, map and model scales, aspect ratios, and converting quantities proportionally.