The image above is a circle.

To compute the perimeter or circumference of a circle, one essential parameter is needed and this parameter is the **radius of a circle** (r). You can also use the **diameter of a circle** to compute the area of a circle (d).

The formula for calculating the perimeter or circumference of a circle is:

P = 2πr

Where:

P = Perimeter or Circumference of a circle

r = Radius of a circle

Let’s solve an example:

Find the perimeter or circumference of a circle where the radius of a circle is 8 cm.

This implies that;

r = Radius of a circle = 8 cm

P = 2πr

P = 2 x 3.142 x 8

P = 50.265

Therefore, the **perimeter or circumference of a circle** is **50.265 cm.**

**Calculating the Area of a Circle using the Diameter of a Circle.**

The formula is P = πd

Where:

P = Perimeter or Circumference of a circle

d = Diameter of a circle

Let’s solve an example:

Find the perimeter or circumference of a circle where the diameter of a circle is 10 cm.

This implies that;

d = Diameter of a circle = 10 cm

P = πd

P = 3.142 x 10

P = 31.42

Therefore, the **perimeter or circumference of a circle** with diameter is **31.42 cm.**

**How to Calculate Radius of a Circle when Perimeter or Circumference of the Circle is Given**

r = ^{P} / _{2π}

where;

r = Radius of a circle

P = Perimeter or Circumference of a circle

Let’s solve an example:

Find the radius of a circle where the perimeter or circumference of the circle is 16 cm.

This implies that;

P = Perimeter or Circumference of the circle = 16 cm

r = ^{P} / _{2π}

r = ^{16} / _{6.284}

r = 2.55

Therefore, the **radius of the circle** is **2.55 cm.**

**How to Calculate Diameter of a Circle when Perimeter or Circumference of the Circle is Given**

d = ^{P} / _{π}

where;

d = Diameter of a circle

P = Perimeter or Circumference of a circle

Let’s solve an example;

Find the diameter of a circle where the perimeter or circumference of the circle is 20 cm

This implies that;

P = Perimeter or Circumference of the circle = 20 cm

d = ^{P} / _{π}

d = ^{20} / _{π}

d = 6.365

Therefore, the **diameter of the circle** is **6.365 cm.**