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Ratio Calculator

Our online tools will provide quick answers to your calculation and conversion needs. On this page, you can calculate missing number in a proportion. We have made it easy for you to enter numbers that are either directly proportional or inversely proportional to one another.

Direct Inverse




To find the missing element, leave it blank. To check for equivalent ratios, fill up all four fields.

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Proportion calculation

Directly proportional numbers increase or decrease in equal proportions. if a ∝ b, then a = kb, or, a/b = k where k is constant. Therefore, a1 / b1 = a2 / b2.

In inverse proportion, if one number increases, the other decreases and vice versa so that the product of the two numbers remains constant. if a ∝ 1/b, then a×b = k and therefore, a1 × b1 = a2 × b2. To express in ratios, the variables can be re-arranged as to give a1 / a2 = b2 / b1 or a1 / b2 = a2 / b1

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