How the proportion Calculator works
A proportion states that two ratios are equal, and cross multiplication solves it: the product of the means equals the product of the extremes, so X = B × C ÷ A. It is the math behind scaling recipes, reading maps, and converting rates.
A/B = C/X ⇒ X = B × C ÷ A
Example: if 3 cups of flour make 4 servings, then 9 cups make X, where X = 4 × 9 ÷ 3 = 12 servings.
Frequently asked questions
How do I set up a proportion correctly?
Keep the same units in the same positions: if A is flour and B is servings, then C must be flour and X servings. Mixing positions is the classic error.
Is this the same as the rule of three?
Yes, the rule of three is the traditional name for solving a proportion when three values are known.
Does this work for percentages?
Perfectly. A score of 17 out of 20 as a percent is 17/20 = X/100, so X = 85.