Gallons Per Minute (GPM) Calculator: Determine Spray Nozzle and Orifice Size 

Sprayer nozzle or fertilizer orifice selection requires that you know the flow rate or size of tip that you need. This tool will help you quickly and accurately calculate the flow rate required per sprayer nozzle to apply your desired application rate. 

Using This Information

With this information, you can use a sprayer nozzle chart to find a nozzle that will apply this flow rate. For more information, refer to this complete guide to finding a nozzle size, that breaks down using a spray nozzle nozzle chart. If you need help sizing nozzles for a PWM system then refer to this guide. 

Understanding The Formula In This Calculator

We use the GPM formula to determine the spray nozzle or orifice size needed for your specific sprayer and application requirements. The formula looks like this:

And here is what each value in the equation represents:

• GPM (Gallons Per Minute): This is the flow rate of each nozzle on the sprayer. It tells you how many gallons of liquid are being sprayed out of each nozzle every minute.
• GPA (Gallons Per Acre): This is the amount of liquid you want to apply per acre. Your target application rate.
• mph (Miles Per Hour): This is the speed at which you're driving the sprayer, tractor, UTV, etc.
• W (Width in Inches): This is the nozzle spacing from center to center of each nozzle. 
• 5,940: This is a constant number used to convert the units back into a number that is easy to work with. It is a derivative of the different units involved in this formula. The important part is that you know you need to use 5940 in this formula. 

Example Calculation:

You want to apply a rate of 20 gallons per acre. The average speed you will spray at is 5 mph. The distance between each spray nozzle is 20 inches (center to center). 

In this case, you would Input these values into the calculator:

1. GPA: 20
2. Speed: 5
3. Nozzle Spacing: 20

Click "Calculate GPM" and you get:

GPM: Approximately 0.34

This means each nozzle should deliver 0.34 gallons per minute to apply 20 gallons per acre at a speed of 5 mph with nozzles spaced 20 inches apart.

This formula works for broadband spraying applications with overlapping flat fan nozzles as well as solid stream nozzles used on fertilizer bars and applicators. 

Finding a Spray Nozzle

Nozzle size is a major factor when selecting a spray nozzle but it is not the only thing to consider. You also should consult the label on the product you apply for guidance on the specific spray nozzle requirements for your application.

Dultmeier Sales carries a wide range of sprayer nozzles for nearly any application:

• Broadcast
• PWM
• Drift-control
• Pre or Post-emergent
• Contact or systemic
• Soil applied
• Insecticides
• Fungicides
• Herbicides
• Fertilizer

If you are looking for guidance, get in touch with us and we can help you with sizing and finding a sprayer nozzle.