Pre-Emergent Rate Calculator

The label states a rate as lb active ingredient per acre (or oz ai per 1,000 sq ft). This calculator divides that by the formulation's strength to give the product weight per 1,000 sq ft you actually measure at the spreader or sprayer. The math works for any pre-emergent active ingredient, including prodiamine and dithiopyr, at whatever rate and formulation strength the product label specifies.

WDG / granular / fert-impregnated:
  lb ai per 1,000 = lb ai per acre / 43.56
  lb product per 1,000 = lb ai per 1,000 / (% ai / 100)
  product for job = lb product per 1,000 x (area sq ft / 1,000)

Liquid:
  oz ai per 1,000 = lb ai per acre x 16 / 43.56
  fl oz product per 1,000 = oz ai per 1,000 x 8 / lb ai per gal
  product for job = fl oz product per 1,000 x (area sq ft / 1,000)

Rate unit conversion:
  lb ai / acre = oz ai per 1,000 x 43.56 / 16
  43.56 = 43,560 sq ft per acre / 1,000

Worked example: a label that reads 0.75 lb ai per acre for a 65 WDG (65% active ingredient) on 10,000 sq ft: lb ai per 1,000 = 0.75 / 43.56 = 0.01722; lb product per 1,000 = 0.01722 / 0.65 = 0.0265 lb (0.42 oz product per 1,000 sq ft); for the 10,000 sq ft job, that is 0.265 lb of product (4.2 oz). The formulation strength is the only variable between products with the same active ingredient at the same label rate.

The split-application ledger tracks how much active ingredient has been applied this season against the label's annual maximum. If the label caps the active ingredient at a certain lb ai per acre per year and you split that evenly across two applications, the ledger shows zero remaining after the second round. Enter your label's annual maximum and your prior applications to see where you stand.

For the tank step after this rate is decided, the herbicide tank mix calculator converts the product rate into ounces per tank. To calibrate the spreader or sprayer that will deliver it, the sprayer calibration calculator and spreader calibration calculator each size the equipment to the rate. Pricing the round that includes this application is the job of the lawn treatment program pricing calculator.