How triangle area calculator works
The area of a triangle is the space enclosed by its three sides. The simplest formula is area = (base × height) / 2, where the height is the perpendicular distance from the base to the opposite vertex. For a triangle with base 10 and height 6, the area is (10 × 6) / 2 = 30.
When you only know the three side lengths, the area follows from Heron's formula. First find the semi-perimeter s = (a + b + c) / 2, then area = √(s(s−a)(s−b)(s−c)). For sides 3, 4, and 5 the semi-perimeter is 6 and the area is √(6 × 3 × 2 × 1) = 6.
Pick a method, enter your values, and the tool validates the inputs (positive numbers, and for three sides the triangle inequality), then returns the area. The base-and-height method is the one taught in school; Heron's formula is the fallback when you cannot measure a height directly.