Proportion Calculator

Enter three of four values in the ratio A / B = C / D, and our calculator will instantly find the missing one.

If all four values are entered, it will check if the proportion is correct. Perfect for solving math problems, scaling recipes, checking blueprints, or working with any kind of ratios. Fast, accurate, and easy-to-use — no formulas needed!

Proportion Equation: A divided by B equals C divided by D

About the Proportion Calculator

A proportion states that two ratios are equal: A / B = C / D. This calculator helps you solve for the missing value when three values are known.


Why use Proportions?


Proportions are widely used in math, science, finance, recipes, and everyday calculations. For example:


How to use it:

Enter three values and leave one blank to calculate the missing value. If all four values are entered, the calculator will check if the proportion is correct.


Frequently Asked Questions

A proportion states that two ratios are equal. It is usually written as A/B = C/D. If you know three of the values, you can calculate the fourth.
The most common method is cross-multiplication: A × D = B × C. Then you solve for the missing value. This calculator performs that step automatically for you.
Proportions are used in cooking and recipes, map scale conversions, blueprints, statistics, chemistry mixing, finance, and school math problems.
Yes. If you enter all four values, the calculator will tell you whether the ratios form a valid proportion.
Yes — it is a completely free web-based tool that works on any device.