Liquid Fertilizer Rate Calculator (fl oz per 1,000 sq ft)

Calculate fl oz of liquid fertilizer per 1,000 sq ft from the label weight per gallon and nitrogen percentage, then product per tank from sprayer calibration.

How this is calculated

Three steps: density to nitrogen per gallon, then volume per 1,000 sq ft, then tank math from your sprayer calibration.

step 1: lb N per gallon (Virginia Tech 424-035)
  lb N/gal = weight per gallon (lb/gal) x (%N / 100)

step 2: fl oz per 1,000 sq ft
  fl oz/1,000 = (target lb N / 1,000 sq ft) / (lb N/gal) x 128

  (128 = fl oz per US gallon)

the same rate restated per acre:
  fl oz/acre = fl oz/1,000 x 43.56
  gal/acre   = fl oz/acre / 128

total product for the whole area:
  fl oz total = fl oz/1,000 x (area sq ft / 1,000)

step 3: per-tank mix (when calibration is entered)
  area per fill (sq ft) = tank gal / carrier gal per 1,000 x 1,000
  fl oz per tank         = fl oz/1,000 x (area per fill / 1,000)
  tank fills             = ceil(area / area per fill)

Why density is required, not defaulted. The weight per gallon is what bridges the percentage on the label to a volume you can measure. Picking the wrong density moves the fl-oz answer by several ounces per thousand. Read the density from the product label or SDS, or weigh a measured gallon on a scale.

The core ratio is the same as the dry formula. Purdue Turfgrass Science states the weight-based formula as "Desired rate in lbs N / 1000 sq ft ÷ % nutrient = Total fertilizer needed / 1000 sq ft". For a liquid the only extra step is dividing the weight result by the density to get gallons, then multiplying by 128 for fluid ounces. The dry fertilizer rate calculator handles pounds and bags; this page handles fl oz and tank fills.

The per-acre figure is area-independent. It is the same rate in a bigger denominator, just as in the dry calculator: a 5,000 sq ft lawn and a 10-acre site return the same gallons-per-acre number. The total is the only line that moves with area.

Tank math requires your calibration. The calculator needs two numbers from your sprayer: the tank capacity and the carrier volume (water) it puts down per 1,000 sq ft at the nozzle, pressure, and walking speed you actually use. If you have not calibrated, run your sprayer over a measured strip first, or use the sprayer calibration calculator to get that number. Without a carrier rate the tank section stays blank, because a tank fill without a known spray rate is guesswork.

Frequently asked questions

How do you calculate liquid fertilizer rate per 1,000 sq ft?

Two steps. First, multiply the label weight per gallon by the nitrogen percentage as a decimal to get pounds of nitrogen per gallon. Virginia Tech Extension (424-035) works this as "Lb N/gal of fertilizer solution = 10.86 lb/gal x 0.30 lb N/lb of fertilizer = 3.26 lb N/gal." Then divide your target nitrogen rate (lb N per 1,000 sq ft) by that lb-N-per-gallon figure and multiply by 128 (the number of fluid ounces in a US gallon). A 28-0-0 product at 10.65 lb/gal (OSU BAE-1293, Table 1) delivers 2.98 lb N per gallon, so hitting 1.0 lb N per 1,000 sq ft takes about 42.9 fl oz.

How many ounces of 28-0-0 per 1,000 sq ft?

It depends on the product density. OSU BAE-1293 (Table 1) lists 28-0-0 at 10.65 lb per gallon. At that density and a 1.0 lb N per 1,000 sq ft target, the math gives about 42.9 fl oz per 1,000 sq ft. At a lower density the volume rises; at a higher one it drops. The label weight per gallon is the number that moves the answer, which is why this calculator asks for it rather than assuming a single default.

Where do I find the weight per gallon for my liquid fertilizer?

On the product label or the Safety Data Sheet (SDS), usually in the physical-properties section. It is listed as "weight per gallon", "density" in lb/gal, or "specific gravity" (multiply specific gravity by 8.345 to get lb/gal, because 1 kg/L = 8.345 lb/gal). If neither the label nor the SDS states it, you can weigh a measured gallon on a scale. Do not guess: the density is what bridges the nitrogen percentage to a volume you can measure in a graduated cylinder or tank.

How do I figure out how much liquid fertilizer to add per tank?

You need two numbers your sprayer calibration gives you: the tank size in gallons and the carrier volume (water) your sprayer puts down per 1,000 sq ft at the nozzle and speed you run. Divide the tank size by the carrier rate to get the area one fill covers, then multiply the fl-oz-per-1,000-sq-ft rate by that area in thousands. A 4-gallon backpack putting down 1 gallon of carrier per 1,000 sq ft covers 4,000 sq ft per fill, so at 42.9 fl oz per 1,000 you would add about 171.7 fl oz (1.34 gallons) of product per tank.

Sources

Fertilizer Types and Calculating Application Rates (Publication 424-035). Virginia Cooperative Extension (Virginia Tech). Retrieved Oct 18, 2026.
Calculating the Pounds of Fertilizer to Apply. Purdue Turfgrass Science. Retrieved Oct 18, 2026.
How to Calculate the Amount of Fertilizer Needed for Your Lawn (FS839). Rutgers NJAES Cooperative Extension. Retrieved Oct 18, 2026.
Calculating Lawn Fertilizer Rates. UNH Extension. Retrieved Oct 18, 2026.
Using Water to Calibrate Sprayers for Fertilizers and Other Liquid Solutions (BAE-1293, Table 1). Oklahoma State University Extension. Retrieved Oct 18, 2026.

How we choose and check our formulas