Geometry
Area, perimeter, volume, surface area, triangles and coordinate geometry, from the standard forms.
Area Calculator
The area of a rectangle, square, triangle, circle, ellipse, trapezoid, parallelogram, sector or regular polygon, in any unit.
Perimeter Calculator
The distance around a rectangle, square, triangle, circle, ellipse, trapezoid, parallelogram or regular polygon.
Circle Calculator
Enter any one of a circle’s radius, diameter, circumference or area and get the other three, plus a sector, arc and chord.
Triangle Calculator
Solve a triangle from three sides, two sides and the angle between them, or two angles and a side.
Right Triangle Calculator
Solve a right triangle from two legs, a leg and the hypotenuse, or one side and an angle: every side, both angles and the area.
Pythagorean Theorem Calculator
Find the missing side of a right triangle with a² + b² = c², step by step, spot a Pythagorean triple, or check a corner is square.
Volume Calculator
The volume of a box, cube, cylinder, sphere, cone, pyramid, capsule, hemisphere, frustum, tube or triangular prism, in cubic units, litres and gallons.
Surface Area Calculator
The total, side and base surface area of a box, cube, cylinder, sphere, cone, pyramid, capsule, hemisphere, frustum, tube or triangular prism.
Distance Calculator
The straight-line distance between two points in two or three dimensions, with the midpoint, the change in each coordinate and the slope.
Midpoint Calculator
The point halfway between two points in 2D or 3D, or the missing endpoint when you know one end and the midpoint.
Regular Polygon Calculator
The area, perimeter, apothem, circumradius and angles of a regular polygon from its side, apothem or circumradius.
Trigonometry Calculator
Sine, cosine, tangent, cosecant, secant and cotangent of any angle in degrees or radians, exact on the unit circle, or the angle back from a value.
Polar Coordinates Calculator
Convert a point between Cartesian (x, y) and polar (r, θ) coordinates, with the angle in the right quadrant, in degrees and radians.
Geometry is the one part of this site where the formulas are not in dispute. A circle’s area has been πr² for two thousand years, and no source needs checking against a data sheet. What these pages add is getting the surrounding details right: the units, the edge cases and the shapes that look similar but are not. A cone’s surface area uses its slant height, not its vertical height, and using the wrong one returns a number that looks perfectly reasonable. Three sides of 1, 2 and 3 do not make a triangle, and a page that returns an answer anyway is lying to you. A hypotenuse shorter than one of the legs describes nothing at all. Every page here converts to metres internally and back out to whatever you are working in, so a radius in centimetres gives an area in square metres rather than a number that is right in the wrong unit. Where a formula is an approximation — the perimeter of an ellipse has no exact elementary form — the page says so rather than implying a precision the mathematics does not have.