Proportion Calculator
Solve proportion problems: find the missing value in a/b = c/d. Also simplify ratios and scale recipes/formulas.
How to use the Proportion Calculator
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Enter three values — the fourth is calculated automatically.
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Use Simplify mode to reduce a ratio.
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Copy the result.
What is a proportion?
A proportion states that two ratios are equal — for example, 2/3 = x/12 (x = 8). Proportions appear everywhere: scaling recipes (if 200g flour makes 4 servings, how much makes 6?), converting units, calculating drug dosages, and solving similar triangles in geometry. This tool solves for the missing value and can also simplify any ratio to its lowest terms.
Key features
- Solve for the missing value in a/b = c/x
- Simplify any ratio to lowest terms
- Scale values proportionally
- All math runs locally in your browser
Frequently asked questions
How is this different from the Percentage Calculator?
Proportions are a general form — percentages are a specific case where the denominator is 100. Use this for solving ratios that aren't based on 100.
Can it simplify any ratio?
Yes — enter the numerator and denominator of any fraction-like ratio, and it reduces to the lowest whole-number terms using the greatest common divisor.
Is my input stored?
No. The calculation is done entirely in your browser.
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