Lawn Sprayer Calibration Calculator (Herbicide, Boom)

The test-strip method is the turf-native default: spray a measured strip, catch the volume, and divide. It works for a hand-gun or a boom and needs no nozzle-spacing assumption. The boom formula mode is a second path for ag-style users with a known nozzle output, speed, and spacing.

test-strip:
  pass area    = width × distance   (or a measured area)
  rate/1,000   = volume ÷ (pass area ÷ 1,000)

equivalent GPA (both modes):
  GPA          = rate/1,000 × 43.56     (43,560 sq ft/acre ÷ 1,000)

boom formula (Sprayer Guru):
  rate/1,000   = (136 × GPM) ÷ (MPH × spacing_in)
  OPM input first: GPM = OPM ÷ 128

target check (±5% tolerance):
  deviation %  = (rate − target) ÷ target × 100
  |dev| ≤ 5 → on target · > +5 → over · < −5 → under

walking pace (display only, when time given):
  pace mph     = distance ÷ time × (3600 / 5280)

Worked example (test strip): 1.5 gal over a 7 ft × 143 ft pass = 1,001 sq ft → ≈ 1.50 gal / 1,000 sq ft (≈ 65 GPA), matching Holganix's 1.5 gal/1,000 target. Worked example (boom): 0.44 GPM at 4.5 mph on 20-in spacing → (136 × 0.44) ÷ (4.5 × 20) ≈ 0.66 gal / 1,000 (≈ 29 GPA); a clean set 0.2 GPM at 3.0 mph on 20-in → ≈ 0.45 gal/1,000.

136 is the published (rounded) boom constant from Sprayer Guru — the exact unit-collapse is 12000 / 88 ≈ 136.36, about 0.27% off, well inside the ±5% calibration tolerance the tool itself enforces. The ÷ 43.56 GPA bridge and the × 128 fl oz/gal and OPM/GPM bridges are standard. The ±5% "within 5 percent … calibrated accurately" window is closed at the edges (an exact ±5.0% reads as on target). The double-overlap note stays advisory — the tool never auto-halves your rate. Math follows Holganix, Pesticide Environmental Stewardship, and Sprayer Guru (see Sources below).

Calibration is what makes the rest of the spray math honest. The gallons per 1,000 square feet you land on here is the same figure the chemical cost per 1,000 square feet divides by, the tank you build from it is mixed in the herbicide tank-mix calculator, and when those applications are sold as a season rather than a visit, what the treatment program should bill is where the money side lands.