# Perimeter of a circle

 Perimeter P = 2 x π x r

with π (number pi) approximately equal to 3.14
Radius = AO = OB = r
Diameter = AB = 2 r

## Example

Take a circle with radius r = 3 cm
Perimeter P of the circle = 2 x π x r ≈ 2 x 3.14 x 3 ≈ 18.84 cm²

## Definition of a circle

A circle is a closed shape formed by tracing a point that moves in a plane such that its distance from a given point is constant.
When a set of all points that are at a fixed distance from a fixed point are joined then the geometrical figure obtained is called circle.
Radius is the fixed distance between the center and the set of points. It is noted "r".
Diameter is a line segment, having boundary points of circles as the endpoints and passing through the center.

The perimeter of a circle is calculated using the formula 2 x Pi x Radius, or Pi x Diameter.
The radius of a circle is the length of the line from the center to any point on its edge. The diameter is defined as twice the length of the radius of a circle. The diameter is the distance from one point on a circle through the center to another point on the circle.

The perimeter is defined as the circumference of the circle. The circumference of a circle is the length of the curve that encloses that circle.

## Differences between a circle and a disc

A circle is the boundary of a disc.
A disc (also spelled disk) is the region in a plane bounded by a circle.
A disc with center O and radius r is the surface bounded by the circle with center O and radius r.

## Circumference of a circle

The circumference of a circle is the distance around the outside of the circle. A circle's outside boundary is called the circumference. It is like the perimeter of other shapes like squares. The circumference of a circle is the length of the curve that encloses that circle.

How to find the circumference of a circle?

### Calculate the circumference of a circle with the radius

First, multiply the radius by 2 to get the diameter. Then, multiply the result by π (pi is approximately 3.14). It is done, you found the circumference of the circle.

### Calculate the circumference of a circle with the diameter

Multiply the diameter by π (pi is approximately 3.14). It is done, you found the circumference of the circle.