Ratio Calculator

Solve a proportion A : B = C : X for the missing term, with the cross-multiplication shown.

How to solve a proportion

  1. Enter the three known terms of A : B = C : X.
  2. The calculator cross-multiplies to isolate X.
  3. Read the missing value and the worked steps.

Frequently asked questions

How do you solve a proportion?

Cross-multiply: for A : B = C : X, multiply A × X and B × C, set them equal, then divide. So X = (B × C) ÷ A. For example, 2 : 3 = 8 : X gives X = (3 × 8) ÷ 2 = 12.

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