Toolvemi.

Rule of Three Calculator

If A corresponds to B, what does C correspond to? Solve direct and inverse proportions.

Solve the rule of three

Calculated instantly in your browser.

Browser-based
→
→ ?

X—

Enter the values above.

How to use it

  1. Enter A and B, the pair you know, and C, the new value.
  2. Choose direct or inverse. Direct: more means more. Inverse: more means less.
  3. Read X, the missing value.

Examples

  • 4 apples cost 20. 10 apples cost 50 (direct: 20 × 10 ÷ 4).
  • 4 workers take 20 days. 10 workers take 8 days (inverse: 4 × 20 ÷ 10).

Direct proportion: X = B × C ÷ A. Inverse proportion: X = A × B ÷ C. The first value cannot be 0 for a direct proportion, and the third cannot be 0 for an inverse one.

Browse all tools