liminfoSpray Rate Calculator
Free web tool: Spray Rate Calculator
Application Rate
23.76 GPA
Boom Width
10.0 ft
Acres per Tank
2.1
Tanks Needed
20
Total Gallons
950.4
Acres/Hour
6.1
Time to Spray
6.60 hrs
GPA at Different Speeds
| Speed (MPH) | GPA |
|---|---|
| 3 | 39.60 |
| 4 | 29.70 |
| 5 | 23.76 |
| 6 | 19.80 |
| 7 | 16.97 |
| 8 | 14.85 |
| 10 | 11.88 |
GPA = (5940 {'\u00D7'} GPM) / (MPH {'\u00D7'} Nozzle Spacing in inches). 5940 is the conversion constant for gallons per acre.
About Spray Rate Calculator
The Spray Rate Calculator is a precision tool for farmers, agronomists, and agricultural equipment operators who need to calibrate boom sprayers and plan chemical application. Enter six key parameters — nozzle flow rate (GPM), travel speed (MPH), nozzle spacing (inches), number of nozzles, tank size (gallons), and field size (acres) — and the calculator instantly computes application rate in gallons per acre (GPA), effective boom width in feet, acres covered per tank, number of tank refills needed, total gallons required for the field, acres sprayed per hour, and total spraying time.
Accurate spray rate calibration is critical in modern agriculture. Over-application wastes expensive pesticides, herbicides, or fertilizers and risks environmental runoff. Under-application leaves crops vulnerable to pests and weeds. The core GPA formula is: GPA = (5940 × GPM) / (MPH × nozzle spacing in inches), where 5940 is the unit-conversion constant that translates the result into gallons per acre. A speed-versus-GPA comparison table covering 3 to 10 MPH is also generated, allowing operators to quickly evaluate how changing travel speed affects coverage density without recalculating manually.
This tool processes all calculations in real time within your browser using React useMemo hooks. No spray plan data is sent to external servers. The interface is fully responsive for use on tablets or smartphones in the field, and supports dark mode for comfortable outdoor use in bright sunlight. It is particularly useful for pre-season sprayer calibration, mid-season rate adjustments, and planning the number of tank loads needed for a job.
Key Features
- GPA formula: (5940 × GPM) / (MPH × nozzle spacing) calculated in real time
- Boom width computed from number of nozzles and spacing (nozzles × spacing ÷ 12 = feet)
- Acres per tank and total tank loads needed for the entire field
- Total gallons required and estimated hours to complete field application
- Speed-vs-GPA comparison table at 3, 4, 5, 6, 7, 8, and 10 MPH
- Separate inputs for nozzle flow, travel speed, nozzle spacing, nozzle count, tank size, and field size
- Responsive grid layout optimized for tablet and smartphone use in the field
- 100% client-side processing — no spray plan data leaves your browser
Frequently Asked Questions
What is GPA and why does it matter for spraying?
GPA stands for gallons per acre, the measure of how much liquid is applied to each acre of land. It is the fundamental calibration metric for boom sprayers. Applying the correct GPA ensures the active ingredient reaches the target rate specified on the pesticide or fertilizer label. The GPA formula used by this calculator is: GPA = (5940 × GPM) / (MPH × nozzle spacing in inches), where 5940 is the standard conversion constant.
How do I change my spray rate in the field?
GPA is inversely proportional to travel speed: drive faster and GPA decreases; drive slower and GPA increases. You can also change GPA by swapping nozzles to a higher or lower flow rate (GPM), or by adjusting nozzle spacing. The speed-vs-GPA table in this calculator shows exactly how GPA changes at different speeds for your current nozzle setup, helping you quickly find the right speed for your target application rate.
What does boom width mean in this calculator?
Boom width is the total effective spray swath in feet, calculated as (number of nozzles × nozzle spacing in inches) ÷ 12. For example, 24 nozzles at 20-inch spacing gives a boom width of 40 feet. Boom width directly determines how many passes are needed to cover a field and is used to calculate the acres-per-hour spraying rate.
How many tanks will I need to spray my field?
The calculator divides total gallons needed (GPA × field acres) by your tank size to determine the number of tanks required, rounding up to the nearest whole load. For example, if you need 500 gallons total and your tank holds 200 gallons, you will need 3 tank loads. This helps you plan refill stops and estimate total job time.
What is a typical GPA for herbicide application?
Typical application rates vary by chemical and equipment type. Broadcast herbicide application commonly runs 10–20 GPA with ground sprayers. Low-volume applications for some systemic herbicides may be as low as 3–5 GPA. Fungicide and insecticide applications often target 15–25 GPA for good canopy penetration. Always check the product label for the recommended carrier volume range.
Why does the calculator use 5940 as a constant?
The constant 5940 comes from unit conversion: 1 acre = 43,560 square feet, and 1 gallon = 231 cubic inches. Converting the relationship between GPM (gallons per minute), MPH (miles per hour), and nozzle spacing (inches) to gallons per acre produces the factor 5940. Specifically, 5940 = (43,560 sq ft/acre × 12 in/ft) / (5,280 ft/mile / 60 min/hr × 231 in³/gal ÷ 1 in²).
Can I use this calculator for a pull-type sprayer and a self-propelled sprayer?
Yes. The calculator is equipment-agnostic — it works for pull-type boom sprayers, self-propelled high-clearance sprayers, ATV sprayers, and any other boom sprayer where you know the nozzle flow rate (GPM), travel speed (MPH), and nozzle spacing. Simply enter the specifications for your equipment and the calculator produces the correct GPA and coverage estimates.
How do I measure my nozzle flow rate (GPM) for accurate calibration?
To measure actual nozzle flow, catch the output from one nozzle for exactly 60 seconds in a measuring jug while the sprayer is running at operating pressure. The collected volume in ounces divided by 128 gives GPM. Alternatively, collect for 30 seconds and double the result. Repeat for several nozzles across the boom and average the readings. Replace any nozzle that deviates more than 10% from the target flow rate.