The circumference of a circle is calculated using the formula C = 2πr, where C is the circumference and r is the radius of the circle.
If you know the radius of the circle, simply multiply it by 2 and then multiply that result by π (pi). For example, if the radius of the circle is 5 units, the calculation would be:
C = 2 × π × 5 = 10π
This means the circumference of the circle is 10π units. If you have the diameter instead, you can also use the alternative formula C = πd, where d is the diameter of the circle. Remember that the diameter is twice the radius, so both formulas will lead to the same value for the circumference.