What is the spray application rate equation?

• A. GPA= [GPM*5940]/[MPH*W]
• B. GPA = (GPM*W)/(MPH*5940)
• C. GPA = (GPM + 5940) / (MPH*W)
• D. GPA = (GPM * 5940) * (MPH * W)

Answer: (A)

The main idea is that gallons per acre sprayed (GPA) comes from converting the nozzle flow and travel motion into how much area is covered per minute. The correct form is GPA = (GPM × 5940) / (MPH × W), where GPM is gallons per minute per nozzle, MPH is your ground speed in miles per hour, and W is the spray width in inches (the width of the spray pattern across the ground).

The constant 5940 comes from converting units so that you’re relating gallons per minute to acres per minute. If you work through the geometry and unit conversions (feet and inches, miles per hour to feet per minute, and acres per square foot), you end up with GPA = GPM × 5940 / (MPH × W). This shows why increasing the flow or slowing down increases GPA, while increasing width or speeding up decreases GPA.

Other forms that mix up division, addition, or unit placement would not produce gallons per acre and thus are not correct.