Rule of Three Calculator: Solve Proportions
Solve proportional problems with the classic Rule of Three method in 3 simple steps. Perfect for conversions, recipes, and ratio calculations.
Rule of Three Calculator
Solve proportional math problems using the classic rule of three method.
Known Ratio
Target Quantity
Rule of Three Result
Step 1: Known Ratio:3 → 15
Step 2: Find Unit Rate:1 → 5
Step 3: Scale to Target:8 → 40
Result (D):0
Direct proportionality: When quantity increases, total yield/cost increases by the exact same ratio.
What is the Rule of Three?
The Rule of Three is a mathematical method for solving proportion problems in three steps:
Step 1: Set up the known relationship (A → B)
Step 2: Calculate the unit rate (divide by A)
Step 3: Scale to target quantity (multiply by C)