Geometry calculators
Area, perimeter, volume and surface area for plane shapes and solids, triangle solving for every SSS–SSA case, circles, trigonometry and coordinate geometry, each with a drawing to scale.
12 calculators, 103 checked worked examples.
Shapes
- Area and perimeter calculator for 2D shapes
Area and perimeter of 15 plane shapes, from rectangles, triangles and trapezoids to circles, ellipses, regular polygons and rings, drawn to scale.
- Circle calculator: area, circumference and radius
Area, circumference, radius and diameter of a circle from any one of them, plus arc length, chord, sector and segment area for a central angle.
Solids
Triangles
- Right triangle calculator: hypotenuse, sides and angles
Hypotenuse, missing leg, both acute angles, area and perimeter of a right triangle from any two values, using Pythagoras' theorem and SOHCAHTOA.
- Triangle calculator: solve SSS, SAS, ASA, AAS and SSA
Missing sides, angles, area, perimeter, heights, inradius and circumradius of any triangle from three measurements, with both SSA answers.
Trigonometry
Coordinates
- Slope, distance and midpoint calculator: line through two points
Distance, midpoint and slope between two points, the line's equation in slope-intercept, standard and point-slope form, and where two lines meet.
- Circle through three points: centre, radius and equation
Centre, radius and equation of the circle through three points, in standard form (x − h)² + (y − k)² = r² and general form, plus area.
- Polygon area from coordinates: shoelace formula calculator
Area, perimeter and centroid of any simple polygon from its vertex coordinates, using the shoelace (surveyor's) formula with every term shown.
Angles
- Angle converter: degrees, radians, DMS and gradians
Convert angles between decimal degrees, degrees-minutes-seconds (DMS), radians, gradians, turns, arcminutes, arcseconds and milliradians.
- Polygon angle calculator: interior and exterior angles
Sum of interior angles, each interior and exterior angle of a regular polygon and the number of diagonals, from the number of sides or one angle.
- Roof pitch and slope calculator: angle, grade and rise over run
Angle, percent grade and roof pitch (x in 12) from rise and run or from any one of them, with the sloped length and rafter factor.
How to choose a geometry calculator
Distinguish the boundary, face and solid
Perimeter measures a boundary in units of length. Area covers a flat face in squared units, while volume fills a solid in cubed units. For a room floor, choose area; for a container's capacity, choose volume. Surface area counts the faces you would cover or paint. A circle tool takes radius or diameter, and confusing the two changes area by a factor of four. Use the labelled diagram to check what each measurement describes.
Choose the information you actually have
The right-triangle tool assumes a right angle; a general triangle solver supports other angle and side combinations. Some side-side-angle inputs produce two possible triangles, so inspect both solutions instead of choosing one silently. Coordinate tools are useful when measurements are points rather than side lengths. Convert all lengths to a consistent unit before comparing results, and remember that a mathematically exact shape may only approximate an irregular real object.