How to use this pythagorean theorem calculator
Find a missing side of a right triangle using a² + b² = c². Start with the labeled example values, then replace them with the figures for your problem. Keep units consistent. Results update as you type. If an entry is invalid, the result is cleared and the page explains what needs attention, rather than showing a stale answer.
Formula and calculation method
For a right triangle with legs a and b and hypotenuse c, c = √(a² + b²). To find a missing leg, use √(c² − a²). The hypotenuse is the side opposite the right angle and must be longer than either leg. All dimensions must use the same unit.
Worked example
Two legs of length 3 and 4 give a hypotenuse of √(9 + 16) = 5. To recover a missing leg, select missing-leg mode, enter 3 as the known leg and 5 as the hypotenuse. The result is √(25 − 9) = 4.
Assumptions and limitations
The Pythagorean theorem applies to right triangles only. A triangle with no known right angle cannot generally be solved with this formula. Dimensions must be positive. The calculator does not infer units, assess measurement accuracy or round a dimension to a suitable construction tolerance.
Check and keep your result
Check the example by hand before applying the result to your own figures. Download the result to retain the inputs with the output, or use Print for a paper copy. Calculations run locally in your browser and entries are not sent to our server. The website’s advertising services operate separately; see our privacy policy.
Created and calculation-tested by Velour Trends · Updated 8 November 2026. No independent professional review is claimed. Report a calculation issue.