What is the Proportion Calculator?
Solve a proportion A/B = C/X for the missing value using cross-multiplication. From percentages and fractions to logarithms and quadratic equations, these math calculators show exact results — using arbitrary-precision integers wherever whole-number answers can get very large.
How to use the Proportion Calculator
- Enter your a, your b, your c.
- Results update automatically as you type; you can also press Calculate.
- Read the output: x.
- Use the 📊 chart to see the result visually, then copy or share it.
Formula and method
Worked example
With a = 3, b = 4, c = 15, the Proportion Calculator returns x: 20.
Tips for better results
- Use the formula section on each page to check your homework method, not just the answer.
- For very large factorials, combinations and base conversions we use exact big-integer math.
- Floating-point results are rounded to 12 significant digits to remove binary noise.
Frequently asked questions
What does the Proportion Calculator do?
Solve a proportion A/B = C/X for the missing value using cross-multiplication.
How is it calculated?
The Proportion Calculator uses this method: A/B = C/X → X = B × C ÷ A.
Can you show an example?
With a = 3, b = 4, c = 15, the Proportion Calculator returns x: 20.
Is the Proportion Calculator accurate?
Yes. It uses standard formulas and exact constants, and the results are verified by our automated test suite. Values are displayed to up to 12 significant digits.
Is this tool free and private?
Yes — the Proportion Calculator is completely free with no sign-up, and it runs entirely in your browser, so the values you enter are never uploaded to our servers.
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