Circle Perimeter Calculator

What Is a Circle Perimeter Calculator?

The perimeter of a circle is the length of one complete trip around its edge, also called the circumference. The Circle Perimeter Calculator turns a known radius or diameter into the full perimeter and the half perimeter, which is the curved arc of a semicircle. It is handy for fencing, trim, gaskets, and half round shapes.

How the Math Works

The perimeter uses pi with the radius or diameter:

$$P = 2\pi r = \pi d$$

The half perimeter is half of that, giving the length of the curved arc only:

$$\frac{P}{2} = \pi r$$

The straight flat edge of a semicircle is not included in the half perimeter. If you need a full semicircle border, add the diameter to the arc length.

Worked Example

For a circle with a radius of 6 m, the perimeter is:

$$P = 2 \times \pi \times 6 \approx 37.6991 \text{ m}$$

The half perimeter is about 18.8496 m, and a complete semicircle boundary would add the 12 m diameter for roughly 30.8496 m.

Related free tools

Compare with the Circle Length Calculator and the Circle Measurements Calculator. The Circle Calculator covers additional circle properties.