61 free tools
Triangles dominate this collection, deliberately — they are the shape people actually get stuck on. The Right Triangle Missing Leg Calculator recovers an unknown side from the two you know, the Triangle Height Calculator works backward from area and base, and the Isosceles and Equilateral Triangle Area Calculators handle the special cases that fill homework sets. Circles and quadrilaterals get their own tools too, including the Arc Length Calculator, Circle Diameter Calculator, and Rectangle Perimeter Calculator.
Reach for a geometry calculator whenever you know some of a shape's measurements and need the rest: a student mid-problem-set confirming an answer, a woodworker checking that a brace really forms the angle the plan claims, a gardener turning a sketched bed into actual square footage. Enter the dimensions you have; the tool returns the ones you are missing.
The quiet star of the category is the Heron's Formula Calculator. It computes a triangle's area from its three side lengths alone — no height, no angles required. That matters outside the classroom, because in the real world you can nearly always run a tape measure along the edges of a triangular space, but almost never measure its perpendicular height.