Math

Circle Calculator

Enter the radius to get the diameter, circumference and area of a circle.

By TheCalcTools Updated Formula checked and tested

Your numbers

Your results

Diameter
Diameter
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Circumference
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Area
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Circle Calculator by TheCalcTools

How the Circle Calculator works

Enter the radius in any unit.

The circumference is 2π times the radius, and the area is π times the radius squared.

The area is in the square of your unit.

The formula

d = 2rC = 2πr

Worked example

Using the default values shown in the calculator:

Radius (r)5
  1. With r = 5: diameter = 2 × 5 = 10.00.
  2. Circumference = 2 × π × 5 = 31.4159.
  3. Area = π × 5² = 78.5398.

Result:

Diameter10.0000
Circumference31.4159
Area78.5398

Frequently asked questions

What if I know the diameter instead?

Divide it by 2 to get the radius, then enter that.

What units is the area in?

Square units. A radius in centimetres gives an area in square centimetres.

Sources and further reading

Sphere Volume and Surface Area CalculatorEnter the radius to find the volume and surface area of a sphere Arc Length and Sector Area CalculatorEnter the radius and central angle in degrees to find arc length, sector area and chord… Ellipse CalculatorEnter the semi-major and semi-minor axes of an ellipse Triangle Calculator (Solve Any Triangle: SSS, SAS, ASA)Choose what you know and enter the values Triangle Area Calculator (Heron's Formula)Enter three side lengths to find the triangle's area, perimeter and angles Pythagorean Theorem CalculatorSolve for any side of a right triangle using a² + b² = c²

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