Boom Sprayer Calibration Formula

Gallons per Acre = 5940 x Gallons per Minute / Miles per Hour x Width (Nozzle Spacing in Inches)

Ex. Determine the spray rate. The sprayer is moving at a speed of 3.7 MPH. The sprayer has a spray boom that is 60 feet long with 40 nozzles located evenly throughout the boom. Each nozzle is producing a volume of .5 gallons per minute.

Gallons per Minute

Catch water from one spray nozzle for exactly one minute to determine the amount of output. If caught for less than one minute, you will need to divide the total number of gallons caught by the timed number of seconds and multiply it by 60 to determine gallons per minute.

Miles per Hour

If the sprayer is not equipped with a speedometer, measure out a determined length and time to see how long it takes to drive the measured distance. Take your total number of feet and divide it by how many seconds it took to drive the distance. This gives you feet per second, which is used to determine miles per hour in the following equation.
MPH = feet per second x .6818.

Width

Width is the distance between nozzles on the boom. This can be determined by simply measuring between two nozzles. Or if the boom length is known and number of nozzles you may take the boom size and multiply that by 12 inches per foot and divide by the total number of nozzles.

Gallons per Acre (GPA)

First in your equation, put in the factors that are given in the equation. You know the spray rate, .5 GPM, and the speed of travel, 3.7 MPH. 5940 is a constant in the equation that NEVER changes. Find the nozzle spacing and place in the equation.

5940 x .5 / 3.7 x 18 = 44.6 Gallons per Acre

or if a 1000 ft² basis is desired divide Gallons per Acre by 43.56, because this is how many times 1000 goes into 43560.

44.6 / 43.56 = 1.02 Gallons per 1000 ft²

OR

Another, slightly more time consuming, way to calibrate a sprayer is to fill your sprayer with water and completely spray the area desired to determine the number of gallons used. Next, measure off the total area in square feet to determine the size covered by the sprayer. Now that you have total gallons and area covered, you can determine gallons per acre or gallons per ft².

Ex. You have just sprayed an area with water and found that you used 11 gallons out of a 20 gallon sprayer. You measure off the area to find that the area is 12000 ft². Take the number of gallons used, 11, divided by 12, since this is how many times 1000 will go into 12000. This gives you .92 gallons per 1000 ft² on a 1000 ft² basis. If an acre basis is desired then 43560 and divide it into 12000 and multiply that by your number of gallons used. This gives you a figure close to 40 gallons per acre.

Hand Sprayer Calibration

When calibrating a pump type hand sprayer, you need to keep these things in mind - constant pressure, nozzle height and speed. First, measure out a predetermined area that you know the size of. In your sprayer, add one gallon of water and spray out completely. Remember to keep constant nozzle height, pressure and speed anytime you are calibrating or spraying. Record your total area covered, based on the width of spray times length of area times the number of passes made with your sprayer. To that you may determine, on a 1000 ft² or acre basis, your spray rate.

Ex. Mark off an area that is 100 feet long. You make six 3 foot wide passes with one gallon of water. So your determined area is 100 x 6 x 3 = 1800 ft² for one gallon of water. If you decide to use a 1000 ft² basis then your spray rate is .55 gallons per 1000 ft². Or if an acre basis is desired then you must divide 43,560 into 1800 to get 24.2 gallons per acre.