Proportion calculator

Solve the missing numerator in two equal ratios.

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First ratio numerator

First ratio denominator

More inputs and assumptions

Second ratio denominator

Answer

…

For a/b = x/d, the missing numerator x = a × d ÷ b.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Saved scenario

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Formula and assumptions

Use corresponding quantities in the same positions. This assumes a direct proportional relationship and nonzero denominators.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using Proportion calculator

For a/b = x/d, the missing numerator x = a × d ÷ b.

Use corresponding quantities in the same positions. This assumes a direct proportional relationship and nonzero denominators.

Next: Ratio calculator

A worked example

With first ratio numerator = 3, first ratio denominator = 4, second ratio denominator = 20, the missing second numerator is 15.

Next: Factorial calculator

Before you use the result

Use corresponding quantities in the same positions. This assumes a direct proportional relationship and nonzero denominators.

Example results for first ratio numerator

These examples use First ratio denominator: 4; Second ratio denominator: 20. They are reference calculations, not recommended settings.

First ratio numerator	Missing second numerator
1.5	7.5
3	15
6	30

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ToolOctopus. “Proportion calculator.” Updated 2026-09-26. https://tooloctopus.com/proportion-calculator.

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