Geometry calculators
Triangles, circles, rectangles, cylinders, cones, and spheres from lengths you type.
13 tools
In this group
Right triangles: Pythagoras. SSS with Heron and angles: triangle. Circle accepts radius, diameter, circumference, or area. Solids: cylinder, cone, and sphere. Plane helpers live next door: slope, 2D distance, and midpoint.
- Circle Calculator Radius, diameter, circumference, and area. Enter any one; the rest follow with π from this device.
- Circumference to Diameter Calculator Enter exactly one of circumference, diameter, or radius. The page fills the other two using Math.PI from this browser. Area is not on this spoke; use the circle calculator for area.
- Cone Calculator Right circular cone. Volume is one third π r squared h. Slant height is the hypotenuse of r and h. Lateral and total surface follow from that slant. Units are whatever you typed.
- Cylinder Calculator Right circular cylinder: volume, lateral area, and total surface area.
- Ellipse Calculator Enter semi-axes a and b. Area is exactly πab. Perimeter uses Ramanujan's closed-form approximation, not an elliptic-integral solver.
- Heron's Formula Calculator Find the area of any triangle when you know all three sides. Heron's formula uses the semi-perimeter s = (a + b + c) / 2, then area = sqrt(s(s - a)(s - b)(s - c)). Defaults show the classic 3-4-5 right triangle.
- Parallelogram Area Calculator Compute parallelogram area from base and perpendicular height. Enter the adjacent side when you also want perimeter. Area uses A = base × height, not the slanted side alone.
- Regular Polygon Area Calculator Compute area, perimeter, circumradius, and apothem for a regular polygon. Enter integer side count n and equal side length s. Irregular polygons are out of scope.
- Pythagorean Theorem Calculator Solve a² + b² = c². Enter exactly two of a, b, and c.
- Rectangle Calculator Rectangle area, perimeter, and diagonal. A square is the case length = width.
- Sphere Calculator Sphere volume and surface area from radius.
- Trapezoid Area Calculator Enter the two parallel bases and the perpendicular height. Area uses ((a + b) / 2) × h. Add both non-parallel legs when you also want perimeter.
- Triangle Calculator SSS triangle: Heron area, perimeter, all three angles, side class, and acute/right/obtuse.