Rule of Three Calculator
Use this Rule of Three calculator to solve simple proportions. Enter three known values and the calculator will find the missing one using the relationship a : b = c : x.
| Known values | Equation | What is found |
|---|---|---|
| A, B, C | A / B = C / X | X = (B × C) / A |
| A, B, X | A / B = C / X | C = (A × X) / B |
| A, C, X | A / B = C / X | B = (A × X) / C |
| B, C, X | A / B = C / X | A = (B × C) / X |
Tip: Exactly one field should be left empty. If you enter all four values or fewer than three values, the calculator will ask you to fix the input.
Disclaimer: This calculator is for educational and quick estimation purposes. Always check critical calculations manually.