Angles, Circles, Ellipses, Slope

Angle Conversion Calculator for converting seconds, minutes, degrees, mils, grads, radians and revs.
Angles In Circles How to calculate central angles, inscribed angles and angles formed by radii, chords, tangents and secants.
This also explains how to calculate angles that are located outside of a circle formed by 2 tangents, 2 secants or a tangent and a secant.
Central Angle Calculator Calculates a Circle's Central Angle, Radius or Arc Length
Circle Circumference & Area Calculator
CIRCLE Calculator for Radius, Central Angle, Chord, Segment Height, Apothem, Arc Length and Chord Length. If you know two, this calculates the other five as well as the Sector Area, Segment Area and Circle Area.
ARC to CHORD RATIOS a listing from 1° to 180°
Circle Equation Tutorial
Explains equations of the type x² + y² = r²
Circle Equation Calculator
Input 3 points and it calculates a circle's center, radius and equation.
Tutorial: Determining a circle's equation Knowing the circle's center and radius OR Knowing 3 points.
Ellipses
Calculator and tutorial
Exterior Angle Theorem
Slope and Grade Calculator
Geometry in the real world. Explains and calculates how to determine a road grade, the pitch of a roof, etc.

Types of Triangles
A chart showing triangles classified by angles
(acute, right, obtuse) and by sides (equilateral, isosceles, scalene).
Also has triangle area formulas and a triangle area calculator.
Triangle Centers
A tutorial discussing the incenter, circumcenter, centroid, orthocenter and the Euler line.
Triangle Tester
Calculates if 3 sides will form a triangle or not.
Triangle Tester
Input 3 triangle side lengths and this calculates if the sides will form an equilateral, isosceles, acute, right or obtuse triangle.
Ultimate Triangle Calculator
Input 3 triangle sides, 2 sides with the included angle or 2 angles with the included side and this calculates all the other triangle information.
Triangle Height Calculator
Input 3 triangle sides and this calculates all 3 heights all 3 angles and the area.
Tutorial: How to Calculate 3 triangle heights and all 3 angles knowing just 3 sides.
This also explains the Law of Cosines and Heron's Triangle Area Formula.
Side Side Angle Triangle Calculator If you know 2 triangle sides and a nonincluded angle, this calculates the other side and the other 2 angles.
Right Triangles (Pythagorean Theorem)
30 60 90 and 45 45 90 Triangle Calculator


Quadrilateral Calculators

Quadrilateral page Descriptions and graphics discussing 6 different types of quadrilaterals.
Calculator for Squares and Rectangles
Rhombus Calculator
Input side length and either angle and it calculates the area, both diagonals, altitude, perimeter.
Input both diagonals and it calculates the side, area, altitude, perimeter and both angles.
Calculator for Parallelograms
Input two parallelogram sides and one angle and it calculates the area, both diagonals, altitude, perimeter and the angle of intersection of the diagonals.
Input both diagonals and diagonal intersection angle and it calculates area, both sides, altitude, height, perimeter and both angles.
Has parallelogram formulas, equations, Heron's formula, etc.
Quadrilateral Kite Calculator
Trapezoid Calculator
Calculating Trapezoid Area  Tutorial

Solid Geometry Calculators

