Iron Sulfate and Chelated Iron Rate Calculator (Lawn)

One multiplication gets you from a product label to elemental iron delivered. The rest is scaling to your lawn and dividing by the tank.

step 0 (liquid products): convert fl oz to weight oz
  weight oz / 1,000 = fl oz / 1,000 x density lb/gal / 8

step 1: Fe per 1,000 sq ft
  oz Fe / 1,000  = dose oz wt / 1,000 x (Fe% / 100)
  lb Fe / 1,000  = oz Fe / 1,000 / 16

step 2: total product
  total oz wt    = dose oz wt / 1,000 x (area sq ft / 1,000)
  total lb       = total oz wt / 16

step 3: carrier water
  total gal      = carrier gal / 1,000 x (area sq ft / 1,000)

step 4: tank loads (when a tank size is given)
  loads          = ceil(total gal / tank gal)
  leftover       = loads x tank gal - total gal

Worked example (the defaults). 3 oz of a 20% Fe product (ferrous sulfate) per 1,000 sq ft on 5,000 sq ft with 2 gal carrier water per 1,000 sq ft and a 4-gal tank: Fe delivered = 3 x 0.20 / 16 = 0.0375 lb Fe per 1,000 sq ft; total product = 3 x 5 = 15 oz (0.94 lb); carrier = 2 x 5 = 10 gal; tank loads = ceil(10 / 4) = 3 loads (2 gal leftover in the last tank).

Why the dose is an input, not a built-in constant. Iron products span a wide range of formulations: granular ferrous sulfate (heptahydrate about 20% Fe, commercial monohydrate typically labeled around 30% Fe), liquid chelated iron, and combination micronutrient blends. Each has its own label rate and Fe percentage; check the guaranteed analysis. This calculator takes whatever rate and Fe % your product prints and works the math from there.

Ferrous sulfate Fe content. Ferrous sulfate heptahydrate (FeSO4 with 7H2O) has a molecular weight of 278.01 and iron's atomic mass is 55.845, so the stoichiometric Fe content is 55.845 / 278.01 = 20.09%. Commercial monohydrate products (FeSO4 with H2O) are typically labeled around 30% Fe. The guaranteed analysis on your bag may differ; enter the number on your label.

The calculation runs once you fill in the four required fields, and updates live as you change any input. There is no account, nothing is stored, and the CSV, print, PDF and copy-as-text exports are ungated so the spray sheet travels to the truck with you. For the sprayer walk that puts this product down, calibrate your output with the sprayer calibration calculator. When the application is part of a broader fertilization program, the fertilizer rate calculator sizes the N-P-K side of the same visit.