Rule of Three

Solve proportions visually — find the missing fourth value

d = (5 × 10) / 2 = 25
D (result)

25

If A then BA2B5∝If C then ?C10D25

About this calculator

Solve proportions visually using the rule of three. If A is to B as C is to X, this calculator finds X. Widely used in cooking, unit pricing, scaling recipes, and everyday proportional reasoning.

Common examples

  • If 2 is to 5, then 6 is to 15
  • If 3 is to 12, then 7 is to 28
  • If 100 is to 25, then 60 is to 15
  • If 1 is to 3.5, then 4 is to 14
  • If 8 is to 2, then 20 is to 5