Math
Ratio Calculator
Simplify a ratio to its lowest terms, or solve for a missing value in a proportion.
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Result
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Enter numbers above
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Frequently asked questions
How do I simplify a ratio?
Divide both numbers by their greatest common divisor. 12:18 simplifies to 2:3 because 6 divides evenly into both — this calculator does that step automatically.
How do I solve a proportion like 4:9 = 20:?
Cross-multiply and divide: multiply the second and third numbers together, then divide by the first. For 4:9 = 20:?, that's (9 × 20) ÷ 4 = 45. Use the "Solve" tab above for this.
What's the difference between a ratio and a fraction?
A ratio compares two separate quantities (like 3 red marbles to 2 blue ones), while a fraction represents a part of a whole. They use similar math, but a ratio doesn't need to add up to a "total" the way a fraction's numerator and denominator do.