Rule of Three Calculator
The rule of three is a mathematical method for solving proportion problems. If you know three values of a proportion, this calculator finds the unknown fourth value. Available in simple (direct proportions) and inverse modes.
Frequently Asked Questions
What's the difference between simple and inverse rule of three?
In the simple rule of three, quantities are directly proportional: if one increases, the other increases too. For example, more ingredients = more recipe. In the inverse rule, they are inversely proportional: if one increases, the other decreases. For example, more workers = less time.
How do I use this for recipes?
If a recipe for 4 people needs 200g of flour and you want to make it for 6 people, use: A=4, B=200, C=6, Type=Simple. The result will tell you how much flour you need for 6 people.
Can I use decimal numbers?
Yes, you can use any decimal number. For example, for scales 1:2.5 or 0.5 meters, the calculator works correctly with up to 2 decimal places in the result.