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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.
If you know the radius
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


See Derivation of circumference formula
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


See Derivation of circumference formula
If you know the area
If you know the area of a circle, the circumference can be found using the formula
See Derivation of circumference formula
Calculator
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.
Other circle topics
General
Equations of a circle
Angles in a circle
Arcs
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