Proportion Calculator

A proportion calculator solves equations such as a/b = c/d and finds the missing fourth value. It is commonly used for direct proportion, inverse proportion, and rule-of-three problems.

Enter the three known values and select the unknown value. For a direct proportion such as 3/4 = x/8, cross multiplication gives 3 x 8 = 4 x x, so x = 6.

The rule of three is the standard method for solving a direct proportion when three values are known. If 5 kg costs $15, then 8 kg costs 15 x 8 / 5 = $24.

Direct proportion means both quantities move in the same direction. Inverse proportion means one increases while the other decreases, such as more workers needing fewer days.

It is useful for recipe scaling, currency conversion, unit conversion, map scale, speed and distance problems, pricing, and work-rate questions.

The main mistakes are mixing up direct and inverse proportion, placing values in the wrong order, and using inconsistent units on the two sides of the ratio.

Yes. A ratio calculator and a proportion calculator solve the same type of problem: finding a missing value that keeps two ratios equal, such as a:b = c:d.

Proportionality calculator and proportion solver are other names for a proportion calculator. All of them find the missing value in an equation like a/b = c/d using cross multiplication.

Yes. Image and photo scaling follows the same proportion rule: if a photo is 1200 x 800 pixels and you resize the width to 600 pixels, enter 1200, 800, and 600 to find the new height, 800 x 600 / 1200 = 400 pixels.

These terms describe the same method this calculator uses: cross multiplication solves a/b = c/d by multiplying diagonally (a × d = b × c) and dividing to isolate the unknown value.