Triangle Calculator
Area and perimeter of a triangle from its three side lengths.
Formula: Heron's formula: Area = √(s(s−a)(s−b)(s−c))
Worth Knowing
Given three side lengths this uses Heron's formula, an elegant result that finds a triangle's area without needing its height — a genuine convenience when you know the sides but not the angles. There's a built-in validity check hiding here: three lengths only form a triangle if each side is shorter than the sum of the other two (the triangle inequality). Feed in sides that violate it and no real triangle exists, which is why impossible inputs return no area.
How to Use
- Enter Side a into the first field of the Triangle Calculator.
- Fill in the rest: Side b, Side c.
- Your result appears instantly as you type — there's no submit button or page reload.
Formula
Heron's formula: Area = √(s(s−a)(s−b)(s−c))