Rule of Three Calculator

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inverse rule of three

Inverse Rule of Three

In an inverse proportion, the product of quantities is constant: A × B = C × X, so X = A × B / C.

What is an inverse proportion

When one quantity doubles and the other is halved, we have an inverse proportion. Example: speed and time for a fixed distance.
4 machines finish a job in 6 days. With 8 machines: X = 4 × 6 / 8 = 3 days.

Examples

Machines × Days

Input: A=4, B=6, C=8
Expected output: X = 3

8 machines finish in 3 days.

Safe use

Input: context + tool result
Expected output: interpreted with limits and next steps

Use the result as technical or educational support, keeping the tool limits explicit in the workflow.

Full tool FAQ

What is a direct rule of three?

In a direct proportion, two quantities grow or shrink together: doubling one doubles the other. You set up A/B = C/X and isolate the unknown with X = B × C / A. For example, if 3 workers produce 6 items per day, 5 workers produce X = 6 × 5 / 3 = 10 items, because more labor yields more output in the same proportion.

What is an inverse rule of three?

How do I tell direct from inverse?

What is a compound rule of three?

Can I use decimal values?

What happens if I divide by zero?

How do I use it for unit conversion?

Does the tool round the result?

Frequently asked questions

What is a constant product?

In inverse proportion, A × B = C × X = k (constant). k is the invariant of the relationship.

Does this page replace official or professional review?

No. It helps explain the scenario and use the tool more safely, but real decisions should consider official sources, full context and qualified guidance when needed.

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