Area of a circle in terms of radius: Area = π·r 2 = 3.14·4.1 2 = 52.81 square miles (*) Area of a circle in terms of diameter: Area = π· (d2) 2 = 3.14· (8.22) 2 = 3.14· (4.1) 2 = 52.81 square miles (*) Area of a circle in terms of circumference: Area = C2 4π = 25.762 4π = 663.58(4·3.14) = 663.5812.56 = 52.81 square miles (*)