1) Mark the spot where the sprayer is parked when filling the tank with water. Know the total volume of the tank and the effective boom width.
2) Spray a measured distance on a paved surface, driving at the tractor speed you will use in the field. Note the spray tank pressure.
3) Return to the same spot where the tank was originally filled up and measure the amount required to fill the tank back to the original level.
4) Spray the measured paved surface again and repeat one more time, if necessary.
Example: A spray rig boom is ten feet wide. An acre is equivalent to 43,560 square feet. Because you don't want to take the time to spray an entire acre, reduce the dimensions by one-tenth. Hence, spray a strip 436 feet long.
Multiply the number of gallons needed to fill up the tank by ten to find the amount of carrier that would be used per acre. For example, it if took four gallons to fill up the tank, that would be the equivalent of 40 gallons per acre. Check your figures against the recommended rate for the material you want to use. To each 40 gallons of carrier in the supply tank, add the number of ounces, pints, quarts, gallons, pounds, or grams needed to obtain the recommended application rate.
Follow similar steps to calibrate an orchard or vineyard fan sprayer: Make a trial application with both sides of the sprayer down a test tree or vine row. Return to the same place that the tank was filled with water and refill the tank, measuring the amount needed to refill it. Multiply the number of gallons needed to refill the tank by 43,560 feet squared, the equivalent of an acre. Multiply the length of the test row by the distance between rows and divide that number into the previous number, which will give the actual spray volume.