Slow-release (controlled-release) nitrogen feeds over several weeks and is less likely to burn or leach than quick-release sources.
How the fertilizer calculator works
FertilizerCalc reads the guaranteed analysis on the bag as percentages by weight: nitrogen (N), phosphate (P2O5) and potash (K2O). The pounds of product per 1,000 square feet are your nutrient target divided by that nutrient's percentage as a decimal. That rate times your area in thousands of square feet is the total, rounded up to whole bags; the rate times 43.56 is the amount per acre. The same rate also tells you how much of the other two nutrients you are applying, and how far one bag goes.
Yearly nitrogen by grass type
| Grass | lb N per 1,000 sq ft per year | Type |
|---|---|---|
| Tall fescue | 2–4 | cool-season |
| Kentucky bluegrass | 3–5 | cool-season |
| Perennial ryegrass | 2–4 | cool-season |
| Fine fescue | 1–2 | cool-season |
| Bermudagrass | 3–5 | warm-season |
| Zoysiagrass | 2–3 | warm-season |
| St. Augustinegrass | 2–4 | warm-season |
| Centipedegrass | 1–2 | warm-season |
| Buffalograss | 1–2 | warm-season |
Pounds of product for 1 lb of nitrogen per 1,000 sq ft
| Fertilizer | Per 1,000 sq ft | Per acre |
|---|---|---|
| 46% N (e.g. 46-0-0) | 2.2 lb | 95 lb |
| 32% N (e.g. 32-0-4) | 3.1 lb | 136 lb |
| 29% N (e.g. 29-0-4) | 3.4 lb | 150 lb |
| 24% N (e.g. 24-0-4) | 4.2 lb | 182 lb |
| 16% N (e.g. 16-0-4) | 6.3 lb | 272 lb |
| 10% N (e.g. 10-0-10) | 10 lb | 436 lb |
Ranges are typical US university extension guidance; your local extension office and a soil test give the best numbers for your lawn. Follow the product label and local rules on phosphorus and timing. Results are estimates.
Frequently asked questions
How much nitrogen does my lawn need per year?
Typical ranges are 2–4 lb per 1,000 sq ft for tall fescue, 3–5 for Kentucky bluegrass, 1–2 for fine fescue and centipede, and 3–5 for Bermudagrass.
How do I calculate pounds of nitrogen in a bag?
Multiply the bag weight by the first number as a decimal: a 20 lb bag of 24-0-11 has 20 × 0.24 = 4.8 lb of nitrogen.
Can too much nitrogen hurt grass?
Yes. Heavy feedings can burn the lawn, encourage disease and wash into waterways. Split large amounts into several feedings.
Is FertilizerCalc free?
Yes, with no sign-up or ads.
Are my numbers saved?
Yes, in this browser only.