Difference Between Circumference, Diameter and Radius

Circumference vs Diameter vs Radius

Radius, diameter, and circumference are measurements of three important properties of a circle.

Diameter and Radius

A circle is defined as the locus of a point at a constant distance from a fixed point on a two dimensional plane. The fixed point is known as the center. The constant length is known as the radius. It is the shortest distance between the center and the locus. A line segment starting from the locus passing through the center and end on the locus is known as the diameter.

The radius and the diameter are important parameters of a circle because they determine the size of the circle. To draw a circle, either radius or diameter is only required.

Diameter and radius are mathematically related by the following formula

D = 2r

where D is the diameter and r is the radius.


The locus of the point is known as the circumference. Circumference is a curved line, and its length is dependent on the radius or the diameter. The mathematical relation between radius (or diameter) and circumference is given by the following formula:

C = 2πr = πD

Where C is the circumference and π=3.14. The Greek letter pi (π) is a constant and important in many mathematical and physical systems. It is an irrational number and has the value 3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37510 58209 74944 59230 78164 06286 20899 86280 34825 34211 70679…… In most cases the value of pi up to two decimal places, i.e. π=3.14, is sufficient for considerable accuracy.

Often, in intermediate level school mathematics, above formula is used to define the constant pi (π) as the ratio between the diameter of a circle and its circumference, where its value is approximately given as the fraction 22/7.

What is the difference between Circumference, Radius, and Diameter?

• Radius and diameter are straight lines while circumference is a closed curve.

• Diameter is twice as the radius.

• Circumference is 2π times the radius of the circle or π times the diameter of the circle.