body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
background-color: #f9f9f9;
}
.calculator-container {
background: #ffffff;
padding: 30px;
border-radius: 12px;
box-shadow: 0 4px 15px rgba(0,0,0,0.1);
margin-bottom: 40px;
border-top: 5px solid #2e7d32;
}
.calc-title {
text-align: center;
color: #2e7d32;
margin-bottom: 25px;
font-size: 24px;
font-weight: 700;
}
.input-group {
margin-bottom: 20px;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #555;
}
.input-group input, .input-group select {
width: 100%;
padding: 12px;
border: 1px solid #ddd;
border-radius: 6px;
font-size: 16px;
box-sizing: border-box;
}
.input-group input:focus {
border-color: #2e7d32;
outline: none;
box-shadow: 0 0 0 3px rgba(46, 125, 50, 0.1);
}
.calc-btn {
width: 100%;
background-color: #2e7d32;
color: white;
padding: 15px;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.2s;
}
.calc-btn:hover {
background-color: #1b5e20;
}
.results-area {
margin-top: 25px;
background-color: #e8f5e9;
padding: 20px;
border-radius: 8px;
display: none;
border: 1px solid #c8e6c9;
}
.result-row {
display: flex;
justify-content: space-between;
align-items: center;
margin-bottom: 10px;
padding-bottom: 10px;
border-bottom: 1px solid #c8e6c9;
}
.result-row:last-child {
border-bottom: none;
margin-bottom: 0;
}
.result-label {
font-weight: 600;
color: #2e7d32;
}
.result-value {
font-size: 20px;
font-weight: bold;
color: #1b5e20;
}
.article-content {
background: #fff;
padding: 30px;
border-radius: 12px;
box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}
.article-content h2 {
color: #2e7d32;
margin-top: 30px;
}
.article-content h3 {
color: #444;
}
.formula-box {
background: #f1f8e9;
padding: 15px;
border-left: 4px solid #2e7d32;
font-family: monospace;
font-size: 1.1em;
margin: 20px 0;
}
.note {
font-size: 0.9em;
color: #666;
margin-top: 5px;
}
function calculateAppRate() {
// 1. Get input values
var gpm = parseFloat(document.getElementById('flowRate').value);
var mph = parseFloat(document.getElementById('groundSpeed').value);
var spacing = parseFloat(document.getElementById('nozzleSpacing').value);
var tank = parseFloat(document.getElementById('tankSize').value);
// 2. Validate inputs
if (isNaN(gpm) || isNaN(mph) || isNaN(spacing) || gpm <= 0 || mph <= 0 || spacing 0) {
acresPerTank = tank / gpa;
tankText = acresPerTank.toFixed(2) + " Acres";
}
// 6. Display Results
document.getElementById('results').style.display = 'block';
document.getElementById('res_gpa').innerHTML = gpa.toFixed(2) + " GPA";
document.getElementById('res_gal_mile').innerHTML = gallonsPerMile.toFixed(3) + " Gal/Mile";
document.getElementById('res_acres_tank').innerHTML = tankText;
}
How to Calculate Application Rate for Sprayers
Calculating the correct application rate is the single most critical step in agricultural spraying. Whether you are applying herbicides, fungicides, or liquid fertilizers, ensuring that your equipment delivers the exact amount of chemical per acre is vital for crop health, environmental safety, and cost efficiency. Over-application wastes expensive chemicals and damages crops, while under-application leads to poor pest control.
The Standard Application Rate Formula
In the United States, the standard formula to calculate Gallons Per Acre (GPA) relies on three specific variables: nozzle flow rate, ground speed, and nozzle spacing. The mathematical constant 5940 is used to convert the mix of units (inches, miles, minutes) into a clean GPA result.
GPA = (GPM × 5940) / (MPH × W)
Where:
- GPA: Application Rate in Gallons Per Acre.
- GPM: Flow Rate in Gallons Per Minute (per single nozzle).
- MPH: Ground Speed in Miles Per Hour.
- W: Nozzle Spacing (or spray width per nozzle) in Inches.
- 5940: Unit conversion constant.
Step-by-Step Calibration Guide
1. Measure Nozzle Flow Rate (GPM)
Park your sprayer and run the pump at your target operating pressure. Use a calibration container to catch the output from one nozzle for exactly one minute. The amount of liquid collected in gallons is your GPM. For higher accuracy, measure multiple nozzles and calculate the average.
2. Determine Ground Speed (MPH)
Do not rely solely on your tractor's speedometer, as tire slippage can alter readings. Measure a set distance (e.g., 200 feet) and time how long it takes to drive that distance at your spraying throttle setting. Use the formula: Speed (MPH) = (Distance in Feet × 60) / (Time in Seconds × 88).
3. Measure Nozzle Spacing
Measure the distance between two nozzles on the boom in inches. If you are using a boomless nozzle or a single wand, measure the effective spray width in inches.
Why is the result "GPA" important?
Once you know your GPA (e.g., 15 Gallons Per Acre), you can determine exactly how much chemical to add to your tank. For example, if your chemical label calls for 1 quart of herbicide per acre, and your sprayer is calibrated to 15 GPA:
- For a 300-gallon tank: 300 / 15 = 20 Acres of coverage.
- Chemical needed: 20 Acres × 1 quart = 20 quarts (5 gallons) of herbicide for the full tank.
Troubleshooting Application Rates
If your calculated application rate is not meeting the label requirements (e.g., you are applying 10 GPA but the label requires 20 GPA), you can adjust one of the three variables:
- Change Speed: Driving slower increases GPA; driving faster decreases GPA.
- Change Pressure: Increasing pressure increases flow rate (GPM), but only slightly. To double the flow, you must quadruple the pressure.
- Change Nozzles: This is the most effective way to make large changes in application rate. Switch to a nozzle tip with a larger or smaller orifice size.