How to use Rule of Three Calculator
What Rule of Three Calculator does#
Solve a proportion with the rule of three, both direct and inverse: enter three known values and get the fourth instantly. Great for scaling recipes, conversions and quick maths. 100% in your browser.
How to use it#
- Open the tool and enter your values.
- Adjust any options or units.
- Read the result, calculated as you type.
- Copy or reuse the result wherever you need it.
Your privacy#
Rule of Three Calculator runs entirely in your browser. Your data never leaves your device — there is no upload, and nothing is stored on our servers.
Frequently asked questions
Is Rule of Three Calculator free to use?
Yes. Rule of Three Calculator is completely free and needs no account or sign-up.
Is my data private?
Yes. Rule of Three Calculator works entirely in your browser, so your data never leaves your device.
Do I need to install anything?
No. Rule of Three Calculator runs online in any modern browser, on desktop or mobile.