Proportion Calculator
Solve a proportion of the form a/b = c/d by finding the missing value.
Enter three of the four values, choose which variable to solve for, and leave the chosen field blank. The proportion is a/b = c/d.
What is a Proportion?
A proportion is an equation that states two ratios are equal. It is usually written as a/b = c/d, which means the ratio of a to b equals the ratio of c to d. Proportions are widely used in scaling, unit conversions, recipe adjustments, and similar-triangle problems.
Solving a Proportion
When three values are known, the fourth can be found using cross multiplication, since a/b = c/d implies a × d = b × c. Rearranging gives the formula for each variable:
- Solve for a: a = b × c / d
- Solve for b: b = a × d / c
- Solve for c: c = a × d / b
- Solve for d: d = b × c / a
Tip: Make sure the value you divide by is not zero. For example, with 2/3 = 4/d, solving for d gives d = 3 × 4 / 2 = 6, so 2/3 = 4/6.
Related Calculators
Note: This calculator solves proportions based on the cross-multiplication formulas described. Results are accurate to the precision shown. While we strive for accuracy, please verify important calculations independently. This tool is for educational and informational purposes and should not be the sole basis for financial, academic, or professional decisions.