Circle Calculator

Calculate circle area, circumference, diameter, and radius using various input methods

Circle Calculator

Enter Known Value

From Radius

Radius (r)

Distance from center to edge

Arc and Sector Calculator

Radius

Angle (degrees)

Arc Length: -

Sector Area: -

Circle Properties

Enter a value to see circle calculations.

Circle Formulas

Area: A = πr²

Circumference: C = 2πr = πd

Diameter: d = 2r

Radius: r = d/2

Arc Length: L = rθ (θ in radians)

Sector Area: A = ½r²θ (θ in radians)

About π (Pi)

π ≈ 3.14159... is the ratio of circumference to diameter for any circle. It's an irrational number with infinite decimal places.

Understanding Circles

Circle Basics

A circle is a set of points equidistant from a center point. The radius is the distance from center to edge, diameter spans the full width.

Area vs Circumference

Area measures the space inside the circle (πr²), while circumference measures the distance around the circle's edge (2πr).

Arcs and Sectors

An arc is part of the circumference, a sector is a "slice" of the circle. Both are proportional to the central angle.

Real-World Uses

Circle calculations are used in engineering, architecture, physics, and everyday tasks like calculating material needs for round objects.

Circle Calculator