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Output-rate reference and worked math

Quotable answer

How is gallons per acre calculated for pesticide spraying?

Gallons per acre (GPA) is calculated from a measured catch (how much a nozzle or the whole sprayer puts out over a known time or area) combined with travel speed and the width of ground actually covered, using a constant that converts those field measurements directly into gallons per acre. The exact formula depends on the equipment type, tabled below.

Reference table

Output-rate formula by equipment

Every formula behind the guided calibration workflow, in one table.
Equipment Method Formula
Backpack and handheld sprayer one-one-hundred-twenty-eighth-acre catch test oz caught over 1/128-acre course = GPA
Boom or broadcast sprayer per-nozzle catch test with the 5,940 constant gpm = oz/min / 128; GPA = (gpm x 5,940) / (mph x spacing in.)
Airblast or orchard sprayer total-output catch test with the 495 constant GPA = (gpm x 495) / (mph x row spacing ft)
Granular applicator or spreader weighed catch test over a measured area lb/acre = (lb collected x 43,560) / (length x width, sq ft)
Calculator

Already know your flow rate?

Generalized GPA from total flow

If you already know your equipment's total output in gallons per minute and the effective width it covers, this generalized calculator computes gallons per acre directly, the same relationship the boom and airblast workflows use, generalized to any total flow and width.

GPA = (total flow, gpm, x 5,940) / (mph x width, inches)

Need to run the actual catch test, or convert a label rate once you have your output rate? Use the guided equipment workflows or the standalone mix-rate converter.

Backpack Boom Airblast Granular Mix-rate converter

The pesticide label is the legal controlling document. This tool is a study and planning aid, never a substitute for label directions.

FAQ

Common questions

Frequently asked questions

What is output rate, in plain terms?
Output rate is how much spray mix or granular product your equipment actually puts down per acre, in gallons per acre for liquids or pounds per acre for granular material. It is a measured fact about your specific equipment at its current settings, not a number printed on the equipment or the label.
Why do different equipment types use different constants?
Each constant (5,940 for boom, 495 for airblast, the 1/128-acre relationship for backpack, 43,560 for granular) is doing the same job, converting the units you can actually measure in the field into gallons or pounds per acre, but the measurable inputs differ by equipment, so the constant that makes the units cancel differs too.
Can I use this generalized calculator instead of the guided workflow?
Yes, if you already know your equipment's total flow rate in gallons per minute and the effective width it covers. The guided equipment workflows are for when you need to run the physical catch test itself; this calculator is for when you already have the flow number and just need the gallons-per-acre math.