Ratio Calculator
Simplify a ratio or find the missing value in an equivalent proportion.
About Ratio Calculator
Simplify integer ratios by dividing both sides by their greatest common divisor. Large integers are calculated exactly, up to 100 digits per input. In proportion mode, enter three values and leave one blank in A : B = C : D. Decimal inputs are converted to exact fractions before solving A × D = B × C. B and D cannot be zero. Exact fractions are retained in the result, with a rounded decimal approximation where useful. All inputs and calculations stay in your browser.
Frequently Asked Questions
Simplify mode requires integers. Multiply both values by the same power of 10 first; for example, 1.5 : 2 becomes 15 : 20, then 3 : 4. Proportion mode accepts ordinary decimals directly.
Simplification accepts signed integers and a single zero, but 0 : 0 is undefined. It normalizes the sign so the second value is positive when nonzero. Proportions use division, so their second and fourth values cannot be zero.
Zeros can make the equation contradictory or allow infinitely many values. The tool rejects these cases instead of producing a misleading number.