Lawn Fertilizer Calculator
Calculate how many pounds of lawn fertilizer to apply from the lawn size, nitrogen rate per 1,000 sq ft and bag analysis, plus bags to buy and the spreader rate.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Fertilizer to apply
- 20.8 lb
- Puts down 5 lb of nitrogen on 5,000 sq ft of lawn
- Bags to buy
- 1 bag of 40 lb
- Each bag is 1.9 applications at this rate
- Spreader rate
- 4.17 lb per 1,000 sq ft
- Find this rate on the bag's spreader chart. If unsure, set the spreader to half and make two passes at right angles
- Coverage per bag
- 9,600 sq ft
- At 1 lb of nitrogen per 1,000 sq ft
Lawn Fertilizer formula
Nitrogen needed (lb) = Lawn area (sq ft) / 1,000 x rate (lb N per 1,000 sq ft)
Fertilizer (lb) = Nitrogen needed / (first bag number / 100)
Spreader rate (lb per 1,000 sq ft) = rate / (first bag number / 100)
Coverage per bag (sq ft) = Bag weight / spreader rate x 1,000Worked example
A 120 x 60 ft lawn with an 800 sq ft side yard is 7,200 + 800 = 8,000 sq ft. For a fall feeding at 0.75 lb of nitrogen per 1,000 sq ft with a 29-0-4: 8,000 / 1,000 x 0.75 = 6 lb of nitrogen. 6 / 0.29 = 20.69 lb of product, spread at 0.75 / 0.29 = 2.59 lb per 1,000 sq ft.
A 45 lb bag holds 45 x 0.29 = 13.05 lb of nitrogen, enough for 13.05 / 0.75 = 17.4 thousand sq ft, so it covers 17,400 sq ft or about 2.2 applications on this lawn. Buy one bag and keep the rest for the next feeding.
Quick reference
| Analysis | Product per 1,000 sq ft | Product for 5,000 sq ft | 40 lb bag covers |
|---|---|---|---|
| 10-10-10 | 10.00 lb | 50.0 lb | 4,000 sq ft |
| 16-4-8 | 6.25 lb | 31.3 lb | 6,400 sq ft |
| 24-0-6 | 4.17 lb | 20.8 lb | 9,600 sq ft |
| 29-0-4 | 3.45 lb | 17.2 lb | 11,600 sq ft |
| 32-0-4 | 3.13 lb | 15.6 lb | 12,800 sq ft |
How to calculate lawn fertilizer
Fertilizer recommendations are given in pounds of actual nitrogen per 1,000 square feet, not pounds of product, because every bag has a different strength. Measure the lawn, subtract the house, driveway and beds, and divide by 1,000. Multiply by the nitrogen rate you want, then divide by the first number on the bag as a decimal. A 5,000 square foot lawn at 1 lb of nitrogen with a 24-0-6 needs 5 / 0.24 = 20.8 lb of product.
Retail bags are labeled by coverage, 5,000 or 15,000 sq ft, at the maker's rate of 0.75 to 1 lb of nitrogen; the weight is in small print and runs 12.5 to 18 lb for a 5,000 sq ft bag. At a 0.5 lb feeding the bag goes twice as far. Weigh out the product for the whole lawn before you start so you can tell if the spreader is running heavy or light halfway through. Check the back label for the slow-release share: coated urea or methylene urea listed as slowly available nitrogen feeds for 6 to 8 weeks and can go on at 1 lb. A bag with 20 percent or less slow-release is a quick-release product and stays at 0.5 to 0.75 lb.
Rates, timing and spreader settings
Cool-season lawns (fescue, bluegrass, rye) get about 1 lb in early September and another in late October or early November before the ground freezes. Give them 0.5 to 0.75 lb in late spring and nothing in July heat. Warm-season lawns (Bermuda, zoysia, St. Augustine) are fed from late spring through August while they are growing, and not after Labor Day in the transition zone. Stay at or under 1 lb of nitrogen per application; urea or ammonium sulfate at 1 lb on a dry lawn in 90 F weather burns it in two days. Phosphorus is banned on established lawns in MN, WI, MI, NY, NJ, MD, VA and several other states unless a soil test shows a need or you are seeding. That is why the shelf is full of 24-0-6 and 32-0-4 and short on 10-10-10.
Spreader charts on the bag list a setting for the maker's rate on common spreaders. If your rate differs or the chart does not list your spreader, calibrate: set the spreader low, spread over a measured 1,000 square feet, and weigh what came out. Broadcast spreaders throw 6 to 10 ft, so overlap to the edge of the last throw; a drop spreader lays exactly the hopper width and stripes if you miss by an inch. Two passes at right angles with half the product each avoid stripes and doubled edges. Close the hopper before every turn and start walking before you open it, or the turn spots get a double dose and burn. Refill on the driveway and sweep spills back onto the grass; granules on pavement wash into the storm drain, and Maryland and New Jersey fertilizer law requires the cleanup.
What this calculator leaves out
The result is nitrogen fertilizer only. Not included: a soil test (typically $15 to $30 through the county extension office) that sets phosphorus, potassium and lime needs; lime or sulfur to move pH; pre-emergent, weed and feed or grub control, which are separate products timed by the herbicide, not the nitrogen; the spreader; and the 1/4 in of water to wash granules off the blades. It also assumes a uniform lawn; shaded areas get half the rate.
Mistakes that cost money
- Overlapping passes or refilling mid-lawn doubles the rate; 2 lb of quick-release nitrogen burns stripes in 48 hours that stay brown all season.
- Phosphorus is banned on established lawns in MN, WI, MI, NY, NJ, MD and others; a 10-10-10 fails the rule, 24-0-6 does not.
- Bag spreader settings assume the maker's rate; a different rate or an off-brand spreader needs a calibration pass over 1,000 sq ft, weighed.
- 1 lb of urea or ammonium sulfate nitrogen on a hot, dry lawn burns; quick-release goes on at 0.5 lb, watered in the same day.
- Slow release on the front with 20% slowly available nitrogen on the back is 80% quick; cap it at 0.75 lb per application.
- Weed and feed with a pre-emergent on a lawn you plan to seed: the herbicide blocks grass seed for 8 to 12 weeks too.
Key facts
- The three numbers on a fertilizer bag are the percent by weight of nitrogen, phosphate and potash, so a 50 lb bag of 10-10-10 holds 5 lb of each.
- One pound of actual nitrogen per 1,000 sq ft is the standard maximum for a single application; quick-release urea or ammonium sulfate is held to 0.5 to 0.75 lb in hot weather.
- Most lawns need 2 to 4 lb of nitrogen per 1,000 sq ft per year, split into 2 to 4 applications; fine fescue and shade lawns need the least.
- A 24-0-6 fertilizer goes on at 4.17 lb per 1,000 sq ft to deliver 1 lb of nitrogen, so a 40 lb bag covers 9,600 sq ft.
- Water in fertilizer with about a quarter inch of irrigation, and never apply to frozen ground or right before heavy rain.
Frequently asked questions
Why does my lawn have stripes or burned patches after fertilizing?
Light stripes are missed passes. Brown stripes and dead spots are doubled passes, turns made with the hopper open or a spill, usually with a quick-release product; 2 lb of urea nitrogen in one spot burns in 48 hours. Water heavily to flush the salts, then reseed the dead spots in fall. Next time halve the setting and make two passes at right angles.
How many pounds of 10-10-10 per 1,000 square feet?
10 lb delivers 1 lb of nitrogen. It also delivers 1 lb of phosphate, which an established lawn rarely needs and MN, WI, MI, NY, NJ, MD and VA prohibit without a soil test. A 50 lb bag covers 5,000 sq ft at that rate, or 10,000 sq ft at a half-pound rate.
How much nitrogen does a lawn need per year?
2 to 4 lb per 1,000 sq ft, split into 2 to 4 feedings of no more than 1 lb each. Shady lawns and fine fescue are at the low end, Bermuda and bluegrass at the high end.
How many square feet does a 40 lb bag of fertilizer cover?
It depends on the analysis and rate. A 40 lb bag of 24-0-6 covers 9,600 sq ft at 1 lb of nitrogen per 1,000 sq ft; a 40 lb bag of 32-0-4 covers 12,800 sq ft.
Sources and references
- Calculations Used to Determine the Amount of Fertilizer Needed to Treat Turf (lb N per 1,000 sq ft divided by bag analysis) (Penn State Extension)
- FS839: How to Calculate the Amount of Fertilizer Needed for Your Lawn (Rutgers NJAES)
- Calculating Lawn Fertilizer Rates fact sheet (nitrogen per bag, coverage, spreader calibration) (University of New Hampshire Extension)
- Fertilizing lawns (annual nitrogen rates and timing) (University of Minnesota Extension)
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