Lawn Fertilizer Calculator
How much fertilizer does your lawn need? Enter the area and your fertilizer's N-P-K to get the exact pounds to spread for your target nitrogen rate.
Calculate your fertilizer rate
Most lawns need about 1 lb of nitrogen per 1000 sq ft per feeding.
What N-P-K means
Every fertilizer bag carries three numbers, like 10-10-10 or 24-0-6. These are the guaranteed percentages by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O) — always in that order. A 50 lb bag of 24-0-6 contains 12 lb of nitrogen, 0 lb of phosphate and 3 lb of potash; the rest is carrier material.
| Nutrient | What it does | Deficiency signs |
|---|---|---|
| N — Nitrogen | Drives leaf growth and green color | Pale, yellowish, slow-growing grass |
| P — Phosphorus | Root development and establishment | Purplish tint, poor rooting (rare in established lawns) |
| K — Potassium | Stress, drought and disease tolerance | Weak turf, brown leaf edges |
Nitrogen is the nutrient lawns consume fastest and the one most responsible for that deep green color — which is why lawn fertilizer rates are always calculated from the nitrogen percentage, regardless of the P and K numbers.
Why you dose by nitrogen
Lawn care professionals think in pounds of nitrogen per 1000 square feet, not pounds of product. This normalizes every fertilizer to the same scale: whether you buy 10-10-10 or 29-0-4, the math converts your target nitrogen rate into the product weight that delivers it.
The formula the calculator uses: product (lb) = target N (lb/1000 sq ft) × area (sq ft) ÷ 1000 ÷ (N% ÷ 100). For a 5,000 sq ft lawn targeting 1 lb N/1000 sq ft with 10% nitrogen fertilizer: 1 × 5 × (1 ÷ 0.10) = 50 lb of product. Switch to a 24% nitrogen fertilizer and the same feeding needs only ~20.8 lb — higher-analysis fertilizers simply mean fewer bags to haul.
The 1 lb nitrogen rule
The standard single application for most lawns is about 1 lb of nitrogen per 1000 sq ft. Exceeding this in one pass risks fertilizer burn — brown, crispy patches where concentrated salts desiccated the leaf blades — and pushes weak, disease-prone flush growth.
Annual totals typically run 2–4 lb N per 1000 sq ft, split across the growing season: a spring feeding, an early-summer feeding, and a fall feeding (the most important one for cool-season grasses, since fall nitrogen builds roots rather than top growth). Sandy soils leach nitrogen faster and sit at the higher end; if you mulch-mow and return clippings, you can cut the total by roughly a third since clippings return about 1 lb N per 1000 sq ft per year.
Application tips
- Split it, don't spike it. Two applications of 0.5 lb N beat one of 1 lb for steady growth — smaller, more frequent feedings are always safer.
- Use a calibrated spreader. Eyeballing from the bag leads to stripes and burn spots. Set the spreader to the bag's recommended setting for your target rate and walk at a steady pace with slight overlap.
- Water it in. Apply roughly ¼–½ inch of irrigation (or time it before rain) to move granules off the leaf blades and into the root zone.
- Skip fertilizing dormant or stressed lawns. Don't feed brown, heat-dormant summer turf or frozen ground — the nutrients wash away unused.
- Soil-test first. A $15 soil test tells you whether you even need phosphorus or potassium; many established lawns need nitrogen only, which saves money and keeps excess P out of waterways.
Frequently asked questions
How much fertilizer per 1000 sq ft of lawn?
It depends on nitrogen content. For 1 lb of nitrogen per 1000 sq ft: 10 lb of 10-10-10, or about 4.2 lb of 24-0-6. The calculator converts any N-P-K for you.
What do the numbers on fertilizer mean?
N-P-K: the percentage by weight of nitrogen, phosphate (Pâ‚‚Oâ‚…) and potash (Kâ‚‚O). A 50 lb bag of 24-0-6 contains 12 lb of nitrogen.
How much nitrogen does a lawn need per year?
Most lawns need 2–4 lb of nitrogen per 1000 sq ft per year, split into 2–4 applications. Returning grass clippings reduces the need by about a third.
Can you over-fertilize a lawn?
Yes. Excess nitrogen burns leaf blades, forces weak growth prone to disease, and pollutes waterways. Never exceed ~1 lb N per 1000 sq ft in a single application.
Should I water after fertilizing?
Yes — about ¼–½ inch of water moves nutrients to the root zone, prevents leaf burn, and reduces runoff.