A circle has a radius of \( r \). Write the formula to calculate the circumference of the circle.

To calculate the circumference of a circle with a radius \( r \), you can use the formula \( C = 2 \pi r \). Here, \( C \) represents the circumference and \( \pi \) (approximately 3.14159) is a constant that relates the circle’s diameter to its radius. In the real world, the circumference can help you determine distances around circular objects, such as the perimeter of circular tracks or the lengths of ropes needed for circular gardens. Imagine needing to wrap a fence around your round backyard; knowing this formula means you can buy just the right amount of fencing without wasting a single inch!