How it works
For A : B = C : X, cross multiplication gives A × X = B × C, therefore X = (B × C) ÷ A.
Proportions and ratios
Rule of Three Calculator
Complete the proportion: if a first quantity corresponds to a second, discover what the new quantity corresponds to.
Your result20
12 × 5 ÷ 3 = 20
- Constant of proportionality
- 4
- Cross product
- 12 × 5 = 60
Understanding your result
The missing value keeps the same proportional relationship as the first pair. Doubling the first quantity therefore doubles its corresponding value.
Last verified:
03FAQ
Frequently asked questions
It is a method for finding a fourth value when two ratios are equal. It applies to directly proportional quantities.