Proportion Calculator

What Is a Proportion Calculator?

The Proportion Calculator solves for a missing variable in a pair of equivalent ratios (A/B = C/D). This is often known as the Rule of Three and is incredibly useful for scaling recipes, calculating exchange rates, and resizing images. This free online tool is useful for proportion calculator, ratio proportion calculator, rule of three calculator. Common use cases include recipes, unit rates, scaling, pricing, percentages, and solving missing values in equivalent ratios. It is designed for quick browser-based calculations and is suitable for homework, programming, study, everyday math, and checking results.