Geometry Calculator

Area = π × r². For example, a circle with radius 5 has area = π × 25 ≈ 78.54 square units. The circumference (perimeter) = 2πr.

Use Heron's formula: s = (a+b+c)/2, then Area = √(s(s-a)(s-b)(s-c)), where s is the semi-perimeter. This works for any triangle where you know all three sides.

Perimeter is the total length around the outside of a shape (linear units: cm, ft). Area is the amount of 2D space inside a shape (square units: cm², ft²). Perimeter is like fencing a yard; area is like carpeting it.