Right Triangle Missing Dimension Calculator

Find a right triangle’s hypotenuse from two legs, or its missing leg from a hypotenuse and one leg. Both known sides must be positive.

How to use Right Triangle Missing Dimension Calculator

1. Choose Measurement Unit, then enter First Known Side, Second Known Side without a unit suffix. 2. Choose the matching calculation option. Use the selected ordinary, square or cubic unit for each measurement as explained below; changing the selector relabels inputs and does not convert them. 3. Select Calculate, or press Enter, and read missing side length. 4. Select Select Copy result to copy the answer, or Reset to clear the form.

Why use this tool?

Recover a diagonal or perpendicular side when two sides of a right triangle are known.

How the calculation works

For two legs, hypotenuse = √(a² + b²). For a hypotenuse h and leg a, missing leg = √(h² − a²). In that mode, the larger entered value is treated as h. Results use up to six decimal places. Tiny nonzero results below 0.000001 use scientific notation with six significant digits. Browser floating-point arithmetic can introduce small rounding differences. Inputs and calculated magnitudes must not exceed 9,007,199,254,740,991. Negative physical measurements and arithmetic underflow are rejected. Zero dimensions are treated as a degenerate limit where the formula allows them; divisors and sides of an actual triangle must be positive. Formula reference: https://openstax.org/books/prealgebra-2e/pages/c-geometric-formulas

Example

First Known Side = 6 cm, Second Known Side = 8 cm and Known Sides = Two legs give 10 cm. With 10 cm and 6 cm in Hypotenuse and one leg mode, the missing leg is 8 cm.

Practical tip

Choose the correct Known Sides option. A hypotenuse is always longer than either leg.