About
Use the Rule of Three Calculator for proportion problems.
What is the Rule of Three?
The Rule of Three is a method for solving proportion equations with one unknown value. It is commonly used in pricing, recipes, scaling measurements, and percentage-style comparisons.
Direct and inverse proportion
Direct proportion means values grow or shrink together. Inverse proportion means one value grows while the other decreases. This tool supports both modes.
When to use it
- Find total price from a known unit relationship.
- Scale ingredient quantities up or down.
- Estimate quantities under inverse-rate conditions.