Rule of Three Calculator
Solve direct and inverse proportion problems using the rule of three. Enter three known values and choose the unknown to find the fourth value with a clear step-by-step explanation.
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isCalculator Editorial Team
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Frequently Asked Questions
The Rule of Three is a mathematical method used to solve proportions. If you have three numbers that are related proportionally, you can calculate the fourth missing number. It works for both direct and inverse proportionality.
Select whether the relation is direct or inverse, choose which value (A, B, C, or D) is missing, then fill in the three known values and click Calculate. The tool shows the result and the steps used.
In direct proportion, when one value increases the other increases at the same ratio (A/B = C/D). In inverse proportion, when one value increases the other decreases so their product stays constant (A × B = C × D).
