3/5 = 12/x
3x = 60, so x = 20.
Math & ratios
Proportion Calculator
Solve the missing value in a proportion. Enter any three numbers in a/b = c/d and leave one field blank.
Enter any three values. Leave exactly one field blank and Cuantalia will solve the missing number in a/b = c/d.
Missing value
20Proportion3 / 5 = 12 / 20
Solve equivalent ratios without rearranging formulas
Proportions are useful for scaling recipes, maps, prices, mixtures, rates, and many other everyday comparisons.
How to solve a proportion
If a/b = c/d, cross multiplication gives a × d = b × c. With any three known values, rearrange that equation to find the fourth.
Recipes, scale, rates, and comparisons
Proportions are common whenever two ratios need to stay equivalent.
Frequently asked questions
What is a proportion?
A proportion is an equation stating that two ratios are equal.
Can the missing value be in any position?
Yes. Leave one of a, b, c, or d blank and the calculator solves it.