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Herbicide Application Rate Calculator

Calculate GPA (Gallons Per Acre) and tank mix requirements accurately.

1. Sprayer Calibration (Find Your GPA)

Ground Speed (MPH)

Nozzle Spacing (Inches)

Nozzle Flow Rate (GPM per nozzle)

2. Tank Mix Calculation

Tank Capacity (Gallons)

Herbicide Rate (Units per Acre)

*Units can be Pints, Quarts, or Ounces per acre.

Application Rate (GPA): 0

Acres Covered per Tank: 0

Herbicide per Tank: 0

How to Calculate Herbicide Application Rates

Accurate herbicide application is critical for effective weed control, crop safety, and cost management. Over-application can lead to crop injury and environmental runoff, while under-application results in poor weed control and potential resistance.

The Standard Calibration Formula

The core formula used in this calculator to determine the Gallons Per Acre (GPA) is:

GPA = (GPM × 5940) / (MPH × W)

GPM: Gallons per minute of output per nozzle.
MPH: Ground speed of the sprayer.
W: Nozzle spacing (in inches) for broadcast spraying.
5940: A constant that converts units to acres.

Step-by-Step Guide to Sprayer Calibration

Check Nozzle Output: Fill the tank with water and run the sprayer at the desired pressure. Use a flow meter or catch water from one nozzle for one minute to determine GPM.
Determine Speed: Measure the time it takes to drive a set distance (e.g., 200 feet) in the field with the sprayer loaded. Speed (MPH) = (Distance in feet × 0.68) / Time in seconds.
Measure Spacing: Measure the distance between nozzles on the boom.
Calculate GPA: Use the formula above or our calculator to find out how many gallons of water carrier you are applying per acre.

Calculating the Tank Mix

Once you know your GPA, you can determine how many acres a full tank will cover and how much herbicide to add. To find the herbicide per tank:

Product per Tank = (Tank Capacity / GPA) × Herbicide Rate per Acre

Realistic Example

If you are traveling at 5 MPH, with 20-inch nozzle spacing, and your nozzles produce 0.3 GPM:

GPA Calculation: (0.3 × 5940) / (5 × 20) = 17.82 Gallons Per Acre.
Coverage: With a 500-gallon tank, you cover 28.06 acres (500 / 17.82).
Herbicide: If the label calls for 1.5 Quarts per acre, you need 42.09 Quarts per full tank (28.06 × 1.5).