Proportion Calculator Free is a free online toolkit for solving proportions — from a simple a/b = c/d problem in 10th grade math to a two-proportion z-test in a statistics course. Every calculator on this site is free, works instantly in your browser, and shows its steps, so you can check your homework, plan a survey or scale a recipe with confidence.
What This Site Does
We build focused, single-purpose calculators that do one job well. The Proportion Calculator solves a/b = c/d for any missing term, with an exact fraction, a decimal, steps and a cross-product check. Around it, twelve more tools cover ratios, proportional relationships, direct and inverse proportion, percent proportion, scale, the golden ratio, and the full set of proportion statistics: sample proportion, z-tests, confidence intervals and sample size.
How We Work
All calculations run entirely in your browser using JavaScript. No account is needed, nothing is uploaded to a server, and we do not ask for your name or email to use a calculator. Each tool page also includes a written guide with worked examples, common mistakes and real-world uses, written in plain language for students and self-learners. Our Methodology page explains the formulas and how we check our results.
Accuracy and Corrections
We check every formula against standard textbooks and test each calculator with known answers before publishing. If you ever find a mistake, please tell us through the Contact page — we log every correction on our Corrections page and fix verified errors promptly.
Explore the tools from the homepage, the Math hub or the Statistics hub.