Solve proportions with the rule of three. Free instant calculator.
This rule of three tool lets you solve proportion problems where three values are known and the fourth is missing. It is designed for speed and accuracy, running entirely in your browser with no data sent to any server. Whether you are a student, professional, or simply need a quick answer, this calculator provides instant results with clear explanations. The rule of three states that if a/b = c/x, then x = (b × c) / a. Enter three values and select which position is unknown. The calculator cross-multiplies and divides to find the missing value.
The rule of three states that if a/b = c/x, then x = (b × c) / a. Enter three values and select which position is unknown. The calculator cross-multiplies and divides to find the missing value.
Students solve proportion problems in math and science classes. Cooks scale recipe quantities up or down for different serving sizes. Engineers calculate proportional relationships in design specifications. Business analysts project financial metrics based on known ratios. Pharmacists compute medication dosages based on patient weight.
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Yes, this Rule of Three calculator is completely free with no signup, no account creation, and no usage limits. All calculations run locally in your browser, so your data stays private and results appear instantly.
This calculator uses standard mathematical formulas and internationally recognized conversion factors. Results are displayed with up to six significant digits of precision. For most everyday uses, the results are more than accurate enough.
Yes, the calculator is fully responsive and works on smartphones, tablets, and desktop computers. The interface automatically adjusts to your screen size. Touch inputs and on-screen keyboards work seamlessly.
Once the page has loaded in your browser, the calculator works without an internet connection. All computation happens locally using JavaScript. Bookmark the page for quick access anytime.
This calculator uses standard, well-established formulas that are widely accepted in education, science, and professional practice. The specific formula is explained in the "How it works" section above.