Which formula is used for calculating the circumference of a circle?

The formula for calculating the circumference of a circle is derived from the relationship between the circumference and the diameter. Specifically, the circumference is equal to pi (π) multiplied by the diameter of the circle. This relationship is foundational in geometry and highlights the constant ratio between the circumference and the diameter, known as π, which is approximately 3.14.

Using this formula allows for easy computation of the circumference if the diameter is known. For instance, if the diameter of a circle is 10 units, the circumference can be calculated as 10π, which provides a simple method to arrive at the answer without needing to measure the entire perimeter directly.

The other options do not accurately represent the formula for circumference. One suggests a square relation of diameter, while another is based solely on the radius but lacks the necessary multiplication factor of π. The last option adds π and diameter together, which does not yield a measurement of circumference in any form. Hence, the correct choice effectively conveys the essential relationship between diameter and circumference in circle geometry.