Proportion Calculator

How to Solve a Proportion

A proportion states that two ratios are equal: A : B = C : X. When you know three of the four values, you can find the missing fourth value.

Step-by-step

1. Write the proportion as a fraction: A/B = C/X
2. Cross-multiply: A × X = B × C
3. Solve for X: X = (B × C) ÷ A

Worked example

If 2 pencils cost , how much do 10 pencils cost? Set up 2 : 3 = 10 : X. Cross-multiply: 2X = 30. Divide: X = 15. So 10 pencils cost .

When to use proportions

Proportions are used in recipe scaling, map distances, currency conversion, and any situation where two quantities scale together at a fixed ratio.