ENTFACT-805: Calibrating a Boomless Sprayer: Pints to Gallons Method 

by Ric Bessin and tad campbell, extension entomologist and Extension Specialist
University of Kentucky College of Agriculture

Supplies needed: PPE, measuring tape and/or wheel, stopwatch, 5-gallon buckets, 1” hose 4 ft in length (one
for each nozzle), and measuring pitcher.

• Fill the clean sprayer 1/4 full of water and find a location with terrain similar to what you
  will be spraying
• Determine the width covered by the sprayer in feet. Operate the stationary sprayer at
  desired pressure and engine/PTO RPM. Measure the total width of the spray swath (ft),
  calculate the effective width of the spray swath as 80% of the total width (this accounts for
  needed overlap to provide uniform coverage). The nozzles must be at the same height and
  orientation used during spraying.

• Using the effective spray width, select the travel distance from Table 1 needed to cover
  1/8th acre. If your spray width is not shown, simply divide 5445 (1/8th of an acre) by the
  effective spray width.
• Measure and mark the course length.

• Determine the tractor speed to be used during spraying (RPM & gear). Remember, the
  RPM must remain the same as it was when the spray swath was measured. This may take
  some trial and error.

• Drive the course, using the predetermined gear/RPM. Record the amount of time (seconds)
  it takes to cover the distance. Use a rolling start to be sure the tractor is at operating speed
  for the entire course. Drive the course and record the time at least twice and determine the
  average time.

• With the tractor engine/PTO at the predetermined RPM, engage the sprayer and catch/collect
  the entire spray output for the number of seconds it took to travel the course. Catching
  all of the spray output can be challenging. Place a 1” hose over each nozzle so the output can
  be directed into a collection bucket. The technique may vary depending on your sprayer’s
  nozzle configuration, as a collection bucket may be needed for each nozzle due to the output
  volume. There will be several gallons of spray to be collected.

• Measure the amount of water collected. The number of pints (16 ounces) collected equals
  the sprayers output in gallons per acre (GPA).
   

  

  Pints collected = Gallons per acre (GPA)
   

  Table 1. Set course length based on effective spray width to equal 1/8th of an acre.
  Spray Width (ft) Course Length (ft)

  	Spray Width (ft)	Course Length (ft)
  Value	20	272
  	25	218
  	30	182
  	35	156
  	40	136
  	45	121
  	50	109
  	55	99

  
  Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!
  Issued 4/2025