The size and variation of droplets produced by a spray tip. This is the critical performance characteristic for selecting a spray tip that is suited to a particular application. There are several classification systems in use. The one used in this calculator is the American Society of Agricultural and Biological Engineers (ASABE) S572 standard. It defines several droplet classification categories, six of which are useful for agriculture and horticulture (Very Fine, Fine, Medium, Coarse, Very Coarse, and Extremely Coarse).

• Very Fine sprays are less commonly used because such small droplets are prone to drift unless they are used under special weather conditions or with spray equipment designed for them.
• Fine and Medium are often used for foliar-acting weed control and contact-acting fungicides and insecticides.
• Medium sprays are also often used for systemic-acting fungicides, insecticides and herbicides. Medium sprays are used by default by most applicators when spray quality is not defined by the label.
• Coarse and Very Coarse sprays are often used for systemic and residual herbicides.
• Extremely Coarse sprays are often used for soil-applied herbicides and fertilizers.

US Gallons per Acre – the units of measure for “application rate” common in the United States and some areas of Canada and Mexico. Selecting this as your unit of measure will set the calculator to ask for inputs in US units.

The volume of finished spray applied per treated area (US: US gallons per acre, Metric: liters per hectare). Follow the instructions on the pesticide label to determine an appropriate spray application rate. If a range of application rates are listed, use the rate that matches your situation or consult an agronomist.

High application rates provide more spray per area and can increase spray coverage of the target but require more frequent stopping to refill the sprayer, reducing the area that can be treated in a day. Lower application rates require fewer stops for refilling but require close management of spray quality to maintain adequate coverage of the target.

The forward speed of the spraying equipment. Speed sensors should be calibrated or checked for accuracy regularly. Speed can be checked by timing how long it takes to travel a measured distance:

MPH = feet x 0.682 ÷ seconds

The distance between tips on a broadcast spray boom.

The weight (US) or mass (metric) of the spray solution per unit volume (US: lbs/gal, metric: kg/L). High density liquids like some fertilizers pass through nozzle orifices more difficultly than plain water and low density liquids. This must be considered when determining the spraying pressure needed for a spray tip.