You are standing next to a really big circular lake. You want to measure the diameter of the lake, but you don’t want to have to swim across with measuring tape! You decide to walk around the perimeter of the lake and measure its circumference, and find that it’s 400pi meters.
To find the circumference, you have to multiply the diameter of the lake by pi. Since, the circumference is 400 pi, then it is clear that the diameter is 400 meters.
