Online Rule of Three Calculator
Solve simple rule of three (direct or inverse) automatically and visually. Fill in the values and see the result instantly.
How to use: Fill in 3 values and the result appears automatically. The calculation follows the visual proportion above.
Direct: X = (B × C) ÷ A | Inverse: X = (B × A) ÷ C
Use inverse when the relationship is "the greater A, the smaller X" (e.g., speed × time, workers × days).
What is Rule of Three?
The rule of three is a mathematical method to solve proportion problems. It allows finding an unknown value (X) in an equivalence relationship between two ratios.
- Useful in percentages, recipes, finance, physics, chemistry, engineering, etc.
- Choose "direct" when the quantities are proportional.
- Choose "inverse" when they are inversely proportional.