How it works
Solve any side of a right triangle from the other two sides, with the area and perimeter.
Choose which side is missing: the hypotenuse or one of the legs. Enter the two known sides; the calculator applies the Pythagorean theorem and reports the missing side together with the triangle's area and perimeter. Validation ensures the hypotenuse is longer than either leg.
Formula
a² + b² = c²; c = √(a² + b²); a = √(c² − b²); area = a × b ÷ 2; perimeter = a + b + c.
a, b- Legs of the right triangle (length)
c- Hypotenuse (length)
Examples
- Legs 3 and 4Missing side hypotenuse · a 3 · b 4Hypotenuse 5 · area 6 · perimeter 12
- Leg 5 and hypotenuse 13Missing side leg b · a 5 · c 13Leg b 12 · area 30 · perimeter 30
Frequently asked questions
What if the hypotenuse is not the longest side?
Then the triangle is not right-angled; the calculator rejects the input rather than returning a negative square root.
Does it work with any units?
Yes, as long as both known sides use the same unit. The area is then in that unit squared.
How to read the result
The missing side is exact for Pythagorean triples such as 3-4-5 or 5-12-13, and rounded otherwise.
Limitations
Right triangles only. Angles are not reported; use a trigonometry tool for that.
Source: Pythagorean theorem with standard triangle area and perimeter definitions.