Multiply π by the diameter of the circle. The formula using the radius is 𝑪 = 2π𝒓. This means that 2 is multiplied by π and then multiplied by the radius.

The constant π is traditionally defined as the ratio of a circle's circumference to its diameter. As I pointed out in the first installment of this series, the fact that this is well-defined (i.e ...

The circle, which is more than 300ft in diameter, was cut into a field of oil seed rape by Wilton Windmill at Wilton near Marlborough.