Circle Calculator

Calculate circle radius, diameter, area, circumference, arc length, and sector area instantly with formulas and step-by-step breakdowns.

Calculate Circle Properties

Select any known parameter (Radius, Diameter, Circumference, or Area) to calculate all remaining values.

Select Given Parameter:

Enter Value:

Enter radius and central angle (in degrees) to compute sector area and arc length.

Radius (r):

Central Angle (θ in degrees):

A circle is a 2D shape defined as all points at a fixed distance (radius) from a central point.

Radius (r): The distance from the center point to any point on the edge.
Diameter (d): The longest distance across the circle passing through the center (d = 2r).
Circumference (C): The total perimeter distance around the circle (C = 2πr).
Area (A): The enclosed surface measurement (A = πr²).

The area of a circle is calculated using the formula A = πr², where r is the radius and π is approximately 3.14159.

To find the radius when circumference is known, use r = C / (2π).

A sector is a pie-shaped portion enclosed by two radii and an arc. Arc length is the outer curved distance of that sector.

Chord length is calculated using c = 2r × sin(θ / 2), where θ is the central angle in degrees.

Pi (π) is the constant ratio of a circle's circumference to its diameter, approximately equal to 3.14159265.