Circle

A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre. The distance between any point of the circle and the centre is called the radius.

This article is about the shape and mathematical concept. For other uses, see Circle (disambiguation).
"360 degrees" and "360°" redirect here. For other uses, see 360 degrees (disambiguation).

Circle
A circle
  circumference C
  diameter D
  radius R
  centre or origin O
TypeConic section
Symmetry groupO(2)
AreaπR2
PerimeterC = 2πR
Geometry
Projecting a sphere to a plane
Branches
  • Concepts
  • Features
Dimension
Zero-dimensional
One-dimensional
Two-dimensional
Triangle
Parallelogram
Quadrilateral
Circle
Three-dimensional
Four- / other-dimensional
Geometers
by name
by period
BCE
1–1400s
1400s–1700s
1700s–1900s
Present day

The circle has been known since before the beginning of recorded history. Natural circles are common, such as the full moon or a slice of round fruit. The circle is the basis for the wheel, which, with related inventions such as gears, makes much of modern machinery possible. In mathematics, the study of the circle has helped inspire the development of geometry, astronomy and calculus.

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