Calculate your fertilizer
Your fertilizer plan
Nutrients you will apply
Spreader setting estimator & calibration
Spreader dial numbers mean different things on different brands, so treat these as a starting point only — then calibrate. The estimate is derived from your calculated product rate of 10.00 lb per 1,000 sq ft.
Calibrate in 5 minutes (the 1,000 sq ft test)
- Weigh the product for a 1,000 sq ft test strip — that is exactly your "product per 1,000 sq ft" number above.
- Mark a test area of 1,000 sq ft (e.g. 20 × 50 ft, or 93 m² ≈ 9.65 × 9.65 m).
- Set the dial to the estimate above and walk the strip at your normal pace, overlapping wheel tracks slightly.
- Check the hopper. Empty exactly at the finish line? Perfect. Product left over → open the dial one notch. Ran out early → close it one notch. Repeat once.
- Write the setting on the bag with a marker — you will thank yourself next season.
Label examples (typical — always check your bag)
| Product (example) | Label rate | Drop setting | Rotary setting |
|---|---|---|---|
| Scotts Turf Builder Lawn Food | 4.4 lb / 1,000 sq ft | 7 | 5½ |
| Scotts Turf Builder WinterGuard | 4.4 lb / 1,000 sq ft | 7½ | 6½ |
| Scotts Turf Builder SummerGuard | 4.4 lb / 1,000 sq ft | 7 | 6 |
| Scotts Step 1 Starter Fertilizer | 4.4 lb / 1,000 sq ft | 6½ | 5½ |
Settings above are typical values printed on product labels; your model and granule size may differ — calibrate to be sure.
What do N, P and K actually do?
The three numbers on every fertilizer bag are the percentage by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O). A 10-10-10 bag is 10% of each; the other ~70% is carrier.
Nitrogen — the green maker
Drives leafy, green top growth. The nutrient lawns hunger for most.
- Deficiency: pale/yellowing older leaves, slow growth
- Excess: burnt leaf tips, weak roots, disease-prone turf
- Typical target: 0.5–1 lb per 1,000 sq ft per feeding
Phosphorus — the root builder
Fuels root development, flowering and fruiting; critical for new lawns and seedlings.
- Deficiency: purplish leaves, poor flowering, weak roots
- Note: many established soils already have enough — a soil test beats guessing
- Excess washes into waterways and can lock up iron and zinc
Potassium — the stress shield
Improves drought tolerance, cold hardiness and disease resistance.
- Deficiency: brown leaf edges ("scorch"), weak stems
- Key for fall "winterizer" feedings on lawns
- Typical target: 0.5–1 lb K₂O per 1,000 sq ft alongside nitrogen
Quick lookup: product per 1,000 sq ft at 1 lb N
How many pounds of each common fertilizer deliver 1 lb of nitrogen per 1,000 sq ft. (Divide your own target rate by the N% — same math the calculator runs.)
| Fertilizer (N-P-K) | lb per 1,000 sq ft | g per m² | Best for |
|---|---|---|---|
| 10-10-10 all-purpose | 10.00 | 48.8 | Gardens, new lawns |
| 13-13-13 garden fertilizer | 7.69 | 37.6 | Vegetable gardens |
| 16-16-16 triple | 6.25 | 30.5 | Gardens, shrubs |
| 16-4-8 palm / shrub | 6.25 | 30.5 | Palms, ornamentals |
| 12-24-24 starter | 8.33 | 40.7 | New seed, transplants |
| 24-0-11 slow-release lawn | 4.17 | 20.3 | Established lawns |
| 29-0-4 lawn food | 3.45 | 16.8 | Lawn greening |
| 30-0-4 turf builder type | 3.33 | 16.3 | Lawn greening |
| 32-0-4 high-N lawn | 3.13 | 15.3 | Established lawns |
| 46-0-0 urea | 2.17 | 10.6 | Pro / farm use — burns easily |
| 21-0-0 ammonium sulfate | 4.76 | 23.2 | Alkaline soils (+sulfur) |
How often should you fertilize?
| Grass type | Feedings / year | When | Notes |
|---|---|---|---|
| Cool-season (fescue, bluegrass, ryegrass) | 2–4 | Mainly fall; light spring | Fall feedings build roots for next year |
| Warm-season (bermuda, zoysia, St. Augustine) | 3–5 | Growing season (May–Sep) | Stop 6–8 weeks before first frost |
| Vegetable garden | 2–3 | At planting + mid-season side-dress | 1–2 lb of 10-10-10 per 100 sq ft per feeding |
Golden rule: never apply more than 1 lb of nitrogen per 1,000 sq ft in a single application. Split heavy annual rates into 2–3 feedings 6–8 weeks apart.
Worked examples
Example 1 — 5,000 sq ft lawn, 10-10-10, 1 lb N rate
Answer: 50 lb of 10-10-10 = one 50-lb bag, $35 total.
Example 2 — 2,000 sq ft vegetable garden, 10-10-10, 0.5 lb N rate
Answer: 10 lb of 10-10-10 — about 1 lb per 100 sq ft, the classic garden rate.
Example 3 — 400 m² lawn (metric), 15-15-15, 0.4 kg N per 100 m²
Answer: 10.67 kg of 15-15-15 for the whole 400 m².
Methodology
Core formula. Product needed (lb) = (target nutrient rate ÷ nutrient %) × (area ÷ 1,000). With a 1 lb N target and a 10% N fertilizer: 1 ÷ 0.10 = 10 lb of product per 1,000 sq ft. Nutrients delivered = total product × each percentage. Bags = round up total ÷ bag size (you cannot buy half a bag). Cost = bags × price per bag; cost per lb of nutrient = cost ÷ nutrient delivered.
Metric conversion. 1 lb N per 1,000 sq ft = 0.48824 kg N per 100 m², derived from 1 lb = 0.45359237 kg and 1,000 sq ft = 92.90304 m². The calculator converts your metric target to imperial internally, runs identical math, then displays kilograms.
Assumptions & honest scope. The calculator assumes the target nutrient is the limiting one and that the fertilizer is spread evenly. It does not replace a soil test — if your soil is already high in phosphorus, feeding P₂O₅ on top wastes money and pollutes waterways. Maximum safe single application: 1 lb N per 1,000 sq ft. Spreader settings are estimates; calibrate with the 5-minute test above.