Measure what a sprayer puts out with plain water, then work out the application rate and how much product goes in each tank. Works for boom sprayers and for backpack or handheld sprayers.
Sprayer
Boom calibration
One number per nozzle, separated by commas or spaces. A single number is treated as the average.
Backpack calibration
Product per tank
Always read the label: it sets the rate, the spray volume range, the protective equipment, and the re-entry and harvest intervals, and those differ between states and countries.
Formulas
Gallons per acre = gallons per minute per nozzle × 5,940 ÷ (mph × nozzle spacing in inches). The 5,940 converts units: 43,560 sq ft in an acre, 12 inches in a foot, 88 feet per minute in a mile per hour. In metric, L/ha = L/min per nozzle × 600 ÷ (km/h × spacing in metres).
The rate is inversely proportional to speed, so driving 10% faster than the calibration run puts on about 10% less. Doubling pressure raises nozzle output by only about 41%, since flow rises with the square root of pressure, so speed and nozzle size are the main ways to change the rate.
Nozzle orifices wear wider with use, and a worn nozzle puts out more than the rest and leaves a streak. Replace any nozzle more than 10% off the boom's average, and replace the whole set if the average is more than 10% above the rating printed on the nozzle.
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