5 free online calculators with step-by-step solutions
Pick the right tool for your problem — 2D shapes, 3D solids, proofs, or composite figures.
Start with these essential polygon calculators calculators
A polygon is any closed plane figure with n straight sides. Two universal formulas: interior angles always sum to (n − 2) × 180°, and exterior angles always sum to exactly 360° regardless of n. For regular polygons (all sides + angles equal), each interior angle = (n − 2) × 180° / n and each exterior angle = 360° / n — that's how you instantly know a hexagon has 120° interior angles or an octagon has 45° exterior angles. The calculators below cover regular polygon area (apothem method and side-length method), perimeter, vertex coordinates, irregular polygon area via the Shoelace formula (just enter the vertex list), and angle sums for 3-to-20 sided shapes. For specific n = 3, 4, 5, 6, 8 the dedicated triangle / quadrilateral / pentagon / hexagon / octagon tools are faster.
This collection has 5 polygon calculators: 2 are tagged Most Popular, 3 are supporting tools. The most-used tools include Polygon Angle Sum Calculator, 2D Shapes Calculator.