Crop farming · Spraying
Sprayer calibration in gallons per acre.
Nozzle output, ground speed and nozzle spacing give your application rate in GPA. Also find the nozzle size you need, acres per tank and product per tank.
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Your application rate
Enter the values.
How to calibrate a boom sprayer in gallons per acre
Gallons per acre = nozzle output in gallons per minute × 5,940 ÷ (ground speed in MPH × nozzle spacing in inches). The constant 5,940 comes from the number of square feet in an acre and the unit conversions between feet, inches and minutes. To find the nozzle you need, rearrange it: GPM = GPA × MPH × spacing ÷ 5,940. NC State Extension publishes both formulas.
Worked example. The NC State example: 0.5 GPM per nozzle, 4.5 MPH, 18-inch spacing. GPA = 0.5 × 5,940 ÷ (4.5 × 18) = 2,970 ÷ 81 = 36.67 GPA, or 0.84 gallons per 1,000 sq ft (36.67 ÷ 43.56). To spray 22 GPA at the same speed and spacing you need GPM = 22 × 4.5 × 18 ÷ 5,940 = 0.30 GPM per nozzle. With a 500-gallon tank at 36.67 GPA, one tank covers 13.6 acres, and a 1.5 per acre product rate means 20.5 units in the tank.
Timed speed run. Mark 200 feet, drive it at working speed with the sprayer loaded, and time it. MPH = 200 × 60 ÷ (30.3 × 88) = 4.5. Use the average of several runs.
Always measure real nozzle output, because tips wear and pressure changes the flow. The label sets the product rate and the water volume.
Frequently asked questions
What is the formula for gallons per acre?
GPA = (GPM per nozzle x 5,940) divided by (MPH x nozzle spacing in inches). It is the formula published by NC State Extension for broadcast boom sprayers.
How do I change my GPA?
Change the nozzle size or the pressure (which changes GPM), or change the speed. Speed changes GPA in the opposite direction, so doubling speed halves the rate. Prefer changing nozzles over driving faster.
How do I measure nozzle output?
Run the sprayer at working pressure, catch the flow from a nozzle for one minute (or a fraction of a minute and scale up), and measure it in gallons. Check several nozzles across the boom and replace any that are well off the average.
Does this work for banded spraying?
For banding, replace the nozzle spacing with the width sprayed by each nozzle, as the formula is written for the area each nozzle covers.
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Not professional advice
Pesticide application is regulated and the product label is the law. This tool does the calibration arithmetic only. Follow the label for rates, water volume, nozzle type, protective equipment and restrictions, and consult your local agronomist or extension office. Not professional advice.