Contact Information
971 Coffman Road, Building B
Whitewater, CO 81527

Mailing Address
Department 5087
P.O. Box 20,000
Grand Junction, CO 81502-5001

(970) 255-7121

How to Calibrate a Handgun

Items you will need: measuring tape, flags/paint, bucket, stop watch, measuring container.

  1. Measure and mark an area 18.5 feet by 18.5 feet square.
  2. Fill the sprayer up with water.
  3. Set the pressure at 35 to 40 psi.
  4. Set the desired flow rate of the handgun.
  5. Spray the area marked, keeping the time it takes to spray to wet the area.
  6. Collect in a bucket for the length of time it took to spray the square.
  7. Measure this amount.
  8. This will give you a number in ounces, which is directly equivalent to ____ gallons/acre.
  9. Divide this amount by the gallons in your sprayer. This tells you how much of an acre will be treated with a full sprayer tank.
  10. Multiply this percentage by the per acre rate and you will know how much chemical to put in your tank.

For example:

You have a 25 gallon sprayer
It took you 75 seconds to spray the 18.5’ x 18.5’ area
You collect 150 ounces in the 75 seconds.
Therefore, you are applying 150 gallons/acre
Divide the 150 by 25 gallons (the size of your sprayer) = 1/6 of an acre is being treated by your sprayer.
Now you can take 1/6 of the acre rate of chemical needed and place in your 25 gallon sprayer and know that you are using the correct amount of herbicide

Other techniques for calibration can be found at Weld County Weed Management