Boom Sprayer GPA Calculator
Calibrate a boom sprayer to a target gallons-per-acre rate from nozzle flow, ground speed and nozzle spacing, then size tank loads and chemical for the field.
How This Calculation Works
Gallons per acre equals nozzle flow in gpm times 5,940, divided by ground speed in mph times nozzle spacing in inches. The 5,940 constant folds the unit conversions for gallons, minutes, miles and inches into one number. Acres per tank is tank capacity divided by the resulting GPA, and total carrier is GPA times acres.
Field Calibration & Rate Reference Chart
| Ground speed | Nozzle pressure | Typical GPA | Droplet class |
|---|---|---|---|
| 4 mph | 20 psi | 12 | Coarse |
| 5 mph | 25 psi | 14 | Coarse |
| 6 mph | 30 psi | 15 | Medium |
| 7 mph | 35 psi | 16 | Medium |
| 8 mph | 40 psi | 18 | Medium |
| 9 mph | 45 psi | 19 | Fine |
| 10 mph | 50 psi | 20 | Fine |
| 12 mph | 55 psi | 22 | Fine |
| 14 mph | 60 psi | 24 | Very fine |
| 16 mph | 65 psi | 26 | Very fine |
Common Questions
What is a normal gallons-per-acre rate for a boom sprayer?
Most row-crop burndown and post-emerge passes run 10 to 20 GPA, while dense canopies and soil-applied herbicides often call for 15 to 25 GPA for coverage. The label sets the carrier volume, so treat the label range as the target and calibrate the machine to hit it. Higher GPA improves coverage but cuts acres per tank and raises refill frequency.
Why does the 5,940 constant appear in the GPA formula?
The constant converts nozzle flow in gallons per minute, speed in miles per hour and spacing in inches into gallons per acre in one step. It is derived from 60 minutes per hour, 5,280 feet per mile and 12 inches per foot. Using it keeps the arithmetic to a single division instead of a chain of unit conversions.
How do I find acres per tank?
Divide tank capacity in gallons by the calibrated GPA. A 300-gallon tank at 15 GPA covers 20 acres per fill. Subtract a small headland and turn allowance if you cannot spray the tank dry, and always leave room for the rinse volume you will need at the end of the day.
How often should I recalibrate a boom sprayer?
Recalibrate at the start of each season, after any nozzle or pump change, and whenever you switch to a product with a different carrier requirement. A quick catch test before each major pass catches worn tips early. Keep a written record of flow per nozzle so you can spot drift over the season.