Category: Calculators
Proportion Calculator
Solve A is to B as C is to D
Enter A, B and C in the proportion A is to B as C is to D to solve for the missing value D.
D (A is to B as C is to D)15
D is solved by cross multiplication: D = (B x C) / A.
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What this tool does
A proportion states that two ratios are equal: A is to B as C is to D. Given any three of the four terms, the fourth is found by cross multiplication, D equals B times C divided by A, which is the standard method for scaling recipes, converting measurements and solving similar-triangle problems.
How to use it
- Enter A, the first term of the known ratio.
- Enter B, the second term of the known ratio.
- Enter C, the first term of the second ratio.
- Read D, the missing fourth term.
Privacy
This tool runs entirely in your browser. Your input is never uploaded, stored or shared — closing the tab removes it.
Frequently asked questions
- What is the formula used?
- Cross multiplication: since A / B equals C / D, rearranging gives D = (B x C) / A.
- Why can't A be zero?
- Dividing by A is part of the formula, so A must be non-zero for the proportion to have a defined solution.
- What is a proportion used for?
- Common uses include scaling a recipe up or down, converting between units, working out map distances, and solving for an unknown side in similar triangles.