The formula to find the circumference of a circle given the information we know (the diameter), you could use the circumference formula of c=pi*diameter or: c=3.14 * 4 c=12.56 is the circumference IF THE CIRCLE WAS WHOLE, but since we're working with a semicircle (and in this case, what looks to be exactly 1/2 of a circle), you could divide 12.56 by 2 and come up with 6.28 as the circumference of each of the semicircles.