What formula gives acres to be treated based on pivot radius?

• A. Acres = (pi x r^2) / 43,560
• B. Acres = 2 pi x r
• C. Acres = r^2 / 43,560
• D. Acres = pi x r

Answer: (A)

To determine acres for a circular pivot, you need the area of the circle and then convert square feet to acres. The area of a circle is pi times the radius squared, so with the pivot radius in feet, the area in square feet is pi × r^2. Since one acre equals 43,560 square feet, you convert to acres by dividing by 43,560. So the formula is Acres = (pi × r^2) / 43,560.

The other forms don’t match because they represent different quantities: 2πr gives the circumference (distance around the circle), not area; r^2 / 43,560 omits the pi factor, underestimating the area; and πr has only one factor of r, giving units of length, not area.