Circle Calculator

Calculate radius, diameter, circumference, area, sector area, and arc length of a circle from any known value.

Known Value

Value

Sector Angle (degrees)

Tab to move between fields

Area

78.54

Circumference31.42

Radius5

Diameter10

Sector Area78.54

Arc Length31.42

How to Use This Calculator

Enter any single known circle measurement — radius, diameter, circumference, or area — and all others are derived.
Key relationships: diameter = 2r; circumference = 2πr; area = πr².
For a circular sector, enter the central angle (in degrees) to get sector area and arc length.
Sector area = (θ/360) × πr²; arc length = (θ/360) × 2πr.
The pie chart visualizes the sector vs. remaining arc, which is useful for checking proportional reasoning.
All inputs must be positive; radius and diameter inputs override each other — enter only one at a time.

Ad Placeholder

Formula

A = πr², C = 2πr

Calculate the area and perimeter of common shapes — rectangle, circle, triangle, trapezoid, and ellipse.

Calculate the volume and surface area of common 3D shapes — cube, box, sphere, cylinder, and cone. Convert between units.

Find the missing side of a right triangle using the Pythagorean theorem. Calculate area, perimeter, and angles.

Ad Placeholder