Rule of three calculator
Solve direct or inverse proportions and see the formula used.
If A corresponds to B, what value X corresponds to C?
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How we handle your data →How to use this tool
- Identify what A, B and C represent using consistent units.
- Choose direct or inverse according to the relationship and calculate.
- Check ratios for direct proportions and products for inverse proportions before using X.
An example you can verify
Scale a quantity or compare inversely proportional quantities.
Example input
A: 2 B: 6 C: 3
Expected result
Direct: X=9. Inverse: X=4.
Choose the type based on the actual relationship. Three people take less time than two only at the same work rate.
Settings and limits
If A corresponds to B, enter C to calculate X. For direct proportions, X = B × C / A. For inverse proportions, X = A × B / C. Use consistent quantities and avoid zero denominators.
Frequently asked questions
When should I use an inverse proportion?
When increasing one quantity decreases the other in the same proportion. For example, 2 people take 6 hours; 3 would take 4 hours at the same work rate.