Triangle calculator
In a right triangle the two legs fix everything else: the hypotenuse is the square root of the sum of their squares, and the area is half their product. The legs are the two sides that meet at the right angle.
- Area
- 6
- Perimeter
- 12
- Angle opposite a
- 36.87°
Rates and thresholds
- Hypotenuse
- c = √(a² + b²)
- Area
- S = a × b ÷ 2
- Leg
- a = √(c² − b²)
How do I find the hypotenuse?
Square both legs, add them, and take the square root. With legs of 3 and 4 the hypotenuse is √(9 + 16) = √25 = 5. It is always the longest side and sits opposite the right angle — a result shorter than a leg means something was entered wrong.
How do I calculate a right triangle's area?
Multiply the legs and halve the result: legs of 3 and 4 give an area of 3 × 4 ÷ 2 = 6. In a right triangle the legs are the base and the height, so the hypotenuse plays no part in the area.
Is the 3-4-5 triangle really right-angled?
It is, and you can check it: 3² + 4² = 9 + 16 = 25 = 5². Sides satisfying the Pythagorean equation guarantee a right angle between them. Builders use it to square a corner with a rope; multiples such as 6-8-10 and 9-12-15 work the same way.
Related calculators
- Percentage calculator
- Percentage change calculator
- Discount calculator
- Average calculator
- Circle calculator
- Rectangle calculator