Rule of Three Calculator
Solve direct and inverse proportions with the rule of three.
If
is
then
is
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Given that a value corresponds to another, find the unknown fourth value using cross-multiplication.
How to use
- Enter the known pair and the third value.
- The unknown value is solved automatically.
- Toggle inverse for inversely-proportional problems.
Frequently asked questions
- Direct vs inverse?
- Direct: more of one means more of the other. Inverse: more of one means less of the other.
- How is it calculated?
- Direct: X = B × C ÷ A. Inverse: X = A × B ÷ C.