What is the sprayer calibration formula?

Gallons per acre equals (nozzle flow in GPM times 5,940) divided by (speed in MPH times nozzle spacing in inches). The constant 5,940 converts the mixed units so the answer comes out directly in gallons per acre for a broadcast boom.

Where does the 5,940 constant come from?

It folds together the unit conversions for an acre: 43,560 square feet per acre, 5,280 feet per mile, 12 inches per foot, and 60 minutes per hour. Combining them yields 5,940 when flow is in GPM, speed in MPH, and spacing in inches.

How do I measure nozzle flow rate?

Run the sprayer at working pressure and catch one nozzle's output in a measuring jug for a set time, for example 30 seconds. Convert to GPM: ounces caught divided by 128 gives gallons, then divide by the minutes you caught it. Average several nozzles.

Does this work for banded or directed spraying?

Yes. For broadcast spraying, nozzle spacing is the distance between boom nozzles. For banded spraying over the row, enter the band width instead of nozzle spacing so the rate reflects the actual sprayed area, not the full field.

Why calibrate before every season?

Nozzle tips wear and flow climbs over time, sometimes 10 percent or more, which silently overdoses chemical and wastes money. Pressure regulators drift too. A five-minute calibration check protects efficacy, your budget, and label compliance.

Sprayer Calibration Calculator

Applying the labeled rate depends on knowing your real output, not the number on the rate controller. This calculator uses the standard 5,940-constant sprayer formula to turn measured nozzle flow, ground speed, and nozzle spacing into gallons per acre so you can confirm calibration before any chemical is mixed.

How it works

The broadcast calibration equation is:

GPA = (GPM × 5,940) / (MPH × nozzle spacing in inches)

The constant 5,940 packs the acre unit conversions (43,560 sq ft, 5,280 ft per mile, 12 in per ft, 60 min per hr) into one number, so entering flow in GPM, speed in MPH, and spacing in inches returns gallons per acre directly. Faster speed or wider spacing lowers GPA; higher nozzle flow raises it.

Example and tips

A nozzle flowing 0.30 GPM at 12 MPH on 20-inch spacing gives (0.30 × 5,940) / (12 × 20) = 1,782 / 240 ≈ 7.4 GPA. Catch and average at least four nozzles before trusting one reading, and replace any tip that runs more than 10 percent over the group average. Recheck calibration whenever you change pressure, speed, or nozzle type, because all three move the rate.