How many square meters in a circle 4.2 meters in diameter?

16 square meters, to 2 significant digits. The area of a circle is calculated as the value pi (3.1416...) times the square of the radius of that circle. In this case, where a circle has a diameter of 4.2 meters, the radius, which is half the diameter, will be 2.1 meters. So to solve for the area (A) of this circle: A = pi x r2 = 3.1416 x 2.1m x 2.1m = 15.954456m2 = 16 square meters.