12.56
615.75
3.14159265 square feet.
63.6173 ft2
None. A 12 foot diameter is the length across a circle: it is a linear distance, not an area.
Oh, dude, you're hitting me with some math here! So, the area of a circle is π times the radius squared. If the diameter is 40 feet, the radius is 20 feet. Plug that into the formula, and you get an area of 400π square feet. But who's really counting, right?
450
132.73
346
176.625
12.56
615.75
1590.4
153.93804 square feet.
3.14159265 square feet.
A circle with a diameter of 18 feet has an area of 254.5 square feet.
A circle with a diameter of 24 feet has an area of 452 square feet.