Calibrating Your Sprayer

Calibrating your herbicide sprayers is a good practice for any landowner who participates in noxious weed control. Knowing the output of your sprayer ensures proper herbicide application without the negative effects of too little or too much herbicide in the tank. If you want to see a video demonstration of calibrating a backpack sprayer, click here. We also have a printable version of the guide below.

Follow the steps outlined below.

  1. Establish a plot of land that is 340 square feet.  18.5′ x 18.5′ is the standard layout, but you can use any size as long as it equals 340 square feet.
  2. Fill your sprayer with water and spray the plot. Using a surface that shows when it’s wet, such as gravel or concrete, will make it easier to see where you’ve sprayed. Make sure to spray at a natural speed and constant rate. Have someone time how long it takes you to completely cover the area with water. Repeat this process several times and take an average time.

3. Spray into a container for the length of time that was recorded in step 2, using the same rate and pressure as before. Measure the number of ounces of water in the container after you sprayed for the allotted time frame.

4. The number of ounces collected from the container will equal the gallons per acre (GPA) that the sprayer will deliver.

5. Determine the volume of the sprayer tank.

6. From the pesticide label, determine the amount of pesticide to apply per acre. If you need assistance to figure out the correct amount, feel free to contact CCWP personnel.

7. Calculate the amount of pesticide to add to the spray tank.

Your equation should look like this:

_____oz. per acre (step 6) x (______gallons (step 5) / ______ GPA (step 4))

To see a video demonstration from the Wyoming Weed & Pest Council, click here.