🧮 Rule of Three Calculator
Solve direct, inverse and compound rule of three with full step-by-step calculation.
🔒 100% free – works directly in the browser, no sign-up
Direct Rule of Three
The more A, the more B. Ex: If 5 apples cost $10, how much do 8 apples cost?
X
campo A ↑
campo B ↑
campo C ↑
Inverse Rule of Three
The more A, the less B. Ex: If 4 workers finish a job in 6 days, how many days do 8 workers need?
Compound Rule of Three
Involves 3+ quantities. Ex: 5 machines produce 200 parts in 4 hours. How many parts do 8 machines produce in 6 hours?
Result X (to find)
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Quantity 1 relation:
Quantity 2 relation:
💡 How to use & examples
- Direct: Use when quantities grow together — more workers, more output; more hours, more km driven
- Inverse: Use when one grows and the other shrinks — more machines, less time; more speed, less travel time
- Compound: Use when the problem involves 3+ quantities simultaneously — production with machines and hours at the same time
- Tip: The unknown value (X) should always be in the last quantity position — rearrange data if needed