ENTFACT-804: Calibrating a Boom Sprayer: Ounces to Gallons Method 

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

• Fill the clean sprayer 1/2 full of water and find a location with terrain like what you will be spraying.

• Determine the spacing between nozzles in inches along the boom. 

  

• Using the nozzle spacing, select the travel distance from Table 1 (on reverse side) needed to cover 1/128^th acre by a single nozzle. I would add this in or move the table to the front
• Measure and mark the course length.

• Determintractor speede the tractor speed to be used during spraying (RPM & gear). Remember, the RPM must remain the same as when you will be spraying. 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 in park and the engine/PTO at the predetermined RPM, engage the sprayer and catch/collect the water individually from each nozzle for the number of seconds it took to travel the course. Catch the spray in measuring pitcher. 

  

• Calculate the average nozzle output. Clean or replace any nozzles that are more than 10% above or below the average output.  If any nozzles were cleaned or replaced, repeat the nozzle catch test for all nozzles until they are all within 10% of the average output.

• The average output per nozzle measured in ounces equals the gallons per acre for the boom sprayer.
  
  Average ounces collected per nozzle =  Gallons per acre (GPA)

Table 1. Set course length based on nozzle spacing to equal 1/128^th acre (340 sq ft).

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

Issued 4/2025