How many square feet in a 42 inch diameter circle?

The radius of the circle is 21 inches. The area of the circle is (pi) times (radius squared) = pi times 441 = 1,385.44+ square inches. 1 square foot = 144 square inches. The area of the circle is (1385.44+ square inches) divided by 144 = 9.621 square feet (rounded to 3 decimal places).