Depending on if you know the diameter or the radius the formulas are: Circumference = pi x diameter or pi x 2 x radius
1. 3.14 x 8 ft = 25.12 ft.
2. 3.14 x 2 x 7in. = 3.14 x 14 = 43.96 in.
3. 3.14 x 18 yds. = 56.52 yds.
