Rule of Three Calculator
Solve a proportion instantly: if A corresponds to B, find what C corresponds to.
Result
Result (what C corresponds to)
10.00
How it works
Result = (B × C) ÷ A
The rule of three solves proportions. If A is to B as C is to the result, then Result = B × C ÷ A. Handy for unit prices, recipe scaling, conversions and more.
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Frequently asked questions
What is the rule of three?
It's a method to find an unknown value in a proportion. If A corresponds to B, then C corresponds to (B × C) ÷ A.
Can you give a practical example?
If 3 pens cost 6, how much do 5 pens cost? Set A = 3, B = 6, C = 5 → (6 × 5) ÷ 3 = 10.