Triangle Calculator
Calculate the area and perimeter of a triangle from base and height or three sides.
- Area
- 12
Find a triangle's area from base and height, or from three side lengths using Heron's formula. The three-sides mode also returns the perimeter and validates the triangle inequality.
How to use
- Choose whether to enter base and height, or three side lengths.
- Type the values for your triangle.
- Read the area (and perimeter for three sides) instantly.
Frequently asked questions
- What is Heron's formula?
- With sides a, b, c and semi-perimeter s = (a+b+c)/2, the area equals the square root of s(s-a)(s-b)(s-c).
- Why does it say the triangle is invalid?
- Each side must be shorter than the sum of the other two (the triangle inequality); otherwise no triangle exists.