Home > Circumference

1 Circles

The circumference of a circle can be calculated from its diameter using the formula:

Or, substituting the radius for the diameter:

Where r is the radius and d is the diameter of the circle, and π (the Greek letter pi) is the constant 3.141 592 6...

2 Ellipses

The circumference of an ellipse is more problematical, the exact solution being an infinite series. A good approximation is Ramanujan's:

where and are the ellipse's semi-major and semi-minor axes, respectively. The two are related by the ellipse's eccentricity as follows:

Which means the circumference can also be written as:

1 External link

• Numericana - Circumference of an ellipse