Rule of Three Calculator
Solve a proportion: if A gives B, what does C give?
Input
This tool runs entirely in your browser. The data you paste or load is never uploaded.
Result
Enter your input, then run the tool.
About this tool
Solves a direct or inverse rule of three: if A corresponds to B, find the value that corresponds to C. It shows the cross-multiplication used, which is useful for recipes, prices, conversions and scaling quantities.
How to use it
- Enter A, B and C: “A is to B as C is to X”.
- Choose direct or inverse proportion.
- Read X and the calculation.
Frequently asked questions
When is the proportion inverse?
When one quantity falls as the other rises: if 4 workers need 6 days, 8 workers need 3 days, not 12.
How is X calculated?
Direct: X = B × C ÷ A. Inverse: X = A × B ÷ C.
Keep going
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