Circumference, Perimeter of a circle
From Latin: circum "around" + ferre "to carry"
The distance around the edge of a circle. Also 'periphery' , 'perimeter'.
Try this Drag the orange dots to move and resize the circle. The circumference is shown in blue. Note the radius changes and the circumference is calculated for that radius.

You sometimes see the word 'circumference' to mean the curved line that goes around the circle. Other times it means the length of that line, as in "the circumference is 2.11cm".

The word 'perimeter' is also sometimes used, although this usually refers to the distance around polygons, figures made up of straight line segments.

Given the radius of a circle, the circumference can be calculated using the formula where:
R  is the radius of the circle
π  is Pi, approximately 3.142

If you know the diameter

If you know the diameter of a circle, the circumference can be found using the formula
where:
D  is the diameter of the circle
π  is Pi, approximately 3.142

If you know the area

If you know the area of a circle, the circumference can be found using the formula
where:
A  is the area of the circle
π  is Pi, approximately 3.142

Calculator

 ENTER ANY ONE VALUE Radius clear Diameter clear Area clear Circumference clear

Use the calculator on the right to calculate the properties of a circle.

Enter any single value and the other three will be calculated. For example: enter the radius and press 'Calculate'. The area, diameter and circumference will be calculated.

Similarly, if you enter the area, the radius needed to get that area will be calculated, along with the diameter and circumference.

Related measures

• Radius The radius is the distance from the center of the circle to any point on the perimeter. See radius of a circle.
• Diameter The distance across the circle. See Diameter of a Circle for more.
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