# Everyday Calculation

Free calculators and unit converters for general and everyday use.

Calculators » Math » Proportion - Missing Number

## 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

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

Result window

#### 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