About Rule of Three Calculator
Enter three values in a direct proportion to find the fourth.
How it works
Three known values in a direct proportion determine the fourth by cross multiplication.
How to use
- Enter the first and second related values.
- Enter the third value.
- Read the missing value X.
Practical example
If 2 items cost 10, then 6 items cost 30 at the same unit price.
Useful tips
This is a direct proportion. It does not model inverse proportions, tiered pricing or nonlinear relationships.