The circumference of a circle can be calculated using the formula:
C = π × d
where C is the circumference and d is the diameter of the circle.
In this case, the diameter (d) is 18. Plugging this value into the formula:
C = π × 18
Using the approximate value of π (3.14), we can calculate:
C ≈ 3.14 × 18
C ≈ 56.52
Therefore, the circumference of a circle with a diameter of 18 is approximately 56.52 units.