What formula is used to calculate the circumference of a circle from its diameter?

The formula used to calculate the circumference of a circle from its diameter is expressed as C = Pi * D. In this formula, C represents the circumference, Pi (π) is a mathematical constant approximately equal to 3.14159, and D stands for the diameter of the circle. The relationship indicates that the circumference is directly proportional to the diameter, which means that as the diameter increases, the circumference will also increase in proportion.

This formula effectively captures the geometric property of circles, demonstrating how the circumference is determined by the linear measurement across the widest part of the circle. While there are other formulas related to circles, this particular one specifically connects circumference to diameter, making it the correct choice for the question in focus.

In contrast, the other options provided involve different aspects of circles: one relates to the area of a circle, another involves calculating circumference using the radius (which is related to the diameter but is a separate formula), and the last option describes the relationship between diameter and radius rather than circumference. Each serves a different purpose in circle geometry but does not address the question directly about the relationship between circumference and diameter.