MATH TOOL
Ratio & Proportion Calculator
Solve a simple proportion in the form A : B = C : D. Enter three values and the calculator finds the fourth.
Proportion formula
For A : B = C : D, cross multiplication gives A × D = B × C. Therefore D = (B × C) ÷ A when A is non-zero.
Example
If 2 : 3 = 10 : D, then D = 15.