Rule of Three Calculator
Quickly calculate directly or inversely proportional ratios.
How it works
The simple rule of three helps find a fourth unknown value from three known values that share a directly or inversely proportional relationship.
Frequently asked questions
What is a directly proportional rule of three?
It is a relationship where increasing one quantity causes a proportional increase in the other (e.g., doubling ingredients doubles the servings).
When should I use inverse proportionality?
When increasing one quantity causes a proportional decrease in the other (e.g., increasing a vehicle's speed decreases the travel time).
How does the calculator flag division by zero?
It validates inputs and displays an error alert if the divisor term (A in direct, C in inverse mode) equals zero, which mathematically prevents calculation.