The formula for circumference is C = 2πr, where r is the radius of the circle. However, the radius is half the diameter, so the circumference could also be calculated using the formula C = πd, where d is the diameter of the circle. π is commonly shortened to 3.14.
If the diameter of the circle is 6 feet, an estimate of the circle's circumference is 6 times 3 feet or 18 feet.
