Rule of Three Calculator

Use our free rule of three calculator to solve direct proportions. Given three known values A, B, C in the proportion A : B = C : X, find the unknown X with a clear step-by-step breakdown.

Math

Formula

Solve direct proportions using the rule of three. Given A : B = C : X, the calculator finds X = (B × C) / A with step-by-step explanation showing each calculation.

A : B = C : X → X = (B × C) ÷ A

Percentage: The percentage value you want to apply

Number: The original number or value

Result: The calculated result

How It Works

1Enter A, B, and C (three known values).
2The calculator finds X such that A : B = C : X.
3Click Calculate.

Examples

2 : 4 = 6 : X

1.X = (4 × 6) ÷ 2 = 24 ÷ 2 = 12

Result: 12

5 : 20 = 1 : X

1.X = (20 × 1) ÷ 5 = 20 ÷ 5 = 4

Result: 4

Frequently Asked Questions

A method to solve proportions: if A : B = C : X, then X = (B × C) / A.

No — A and C cannot be zero since division by zero is undefined.

Yes — negative values are supported for all inputs.

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CalculateMe Team

Last updated: 2026-07-15

Rule of Three Calculator

Formula

How It Works

Examples

2 : 4 = 6 : X

5 : 20 = 1 : X

Frequently Asked Questions

What is the rule of three?

Can A or C be zero?

Can the rule handle negative numbers?

Related Calculators

Rule of Three Calculator

Formula

How It Works

Examples

2 : 4 = 6 : X

5 : 20 = 1 : X

Frequently Asked Questions

What is the rule of three?

Can A or C be zero?

Can the rule handle negative numbers?

Related Calculators