In geometry, a large number of facts about circles and their relations to straight lines, angles and polygons can be proved. These facts are called the properties of the circle.

Circles having equal radii are congruent.

Circles having different radii are similar.

The central angle which intercept an arc double of any inscribed angle that intercepts the same arc.

The radius perpendicular to a chord bisects the chord.

The chords equidistant from the center are equal in length.

A tangent to a circle is at right angles to the radius at the point of contact.

Two tangents drawn to a circle from a point out side are equal in length.

The angle subtended at the center of a circle by its circumference is equal to four right angles.

Circumference of two different circles is proportional to their corresponding radii.

Arcs of the same circle are proportional to their corresponding angles.

Radii of the same circle or the equal circles are equal.

Equal chords have equal circumferences.

The diameter of a circle is the longest chord.

Circle which have equal radii are equal.

Equal circles have equal circumference.