Circle Calculator
Calculate radius, diameter, circumference, and area
Parts of a Circle
Center (or origin):
The equidistant point within the circle.
Radius:
Distance from any point on the circle to the center (half the diameter).
Diameter:
Largest distance between two points on a circle, passing through the center (twice the radius).
Circumference:
The distance around the circle.
Arc:
Part of the circumference. Major arc is greater than half, Minor arc is less than half.
Chord:
A line segment connecting two points on a circle (a chord passing through the center is a diameter).
Secant:
A line passing through the circle at two points, extending outside.
Tangent:
A line intersecting the circle at only one point.
Sector:
Area of a circle between two radii. Major sector has central angle > 180°, Minor sector has central angle < 180°.
The figures below depict the various parts of a circle:
The Constant π (Pi)
Pi (π) is a mathematical constant representing the ratio of a circle's circumference to its diameter, approximately 3.14159. It is an irrational and transcendental number, meaning its decimal representation never ends or repeats, and it cannot be expressed exactly as a fraction (though 22/7 is a common approximation).
The historical problem of "squaring the circle" involved attempting to construct a square with the same area as a given circle using only a compass and straightedge. Ferdinand von Lindemann's 1880 proof of pi's transcendence showed this to be impossible.