Lawn Fertilizer Calculator
Calculate exactly how much fertilizer your lawn needs. Enter your lawn area (sq ft or acre), pick a fertilizer (30-0-10, 16-4-8, Milorganite, Urea, or custom NPK), and set your nitrogen rate. Get exact product weight, bags to buy, and total cost — instantly.
30% N · 0% P · 10% K
Results
Never apply more than 1 lb N per 1,000 sq ft in a single application. For higher rates, split into 2 applications 4–6 weeks apart. Water in within 24 hours.
Lawn Fertilizer Formula Explained
The key calculation is working backwards from how much nitrogen (N) you want to apply:
Common Fertilizer Coverage per Bag
| Fertilizer | N% | Bag Size | Coverage @ 1 lb N | Coverage @ 0.5 lb N |
|---|---|---|---|---|
| 30-0-10 | 30% | 40 lb | 12,000 sq ft | 24,000 sq ft |
| 16-4-8 | 16% | 40 lb | 6,400 sq ft | 12,800 sq ft |
| 24-0-6 | 24% | 40 lb | 9,600 sq ft | 19,200 sq ft |
| 46-0-0 Urea | 46% | 50 lb | 23,000 sq ft | 46,000 sq ft |
| 6-4-0 Milorganite | 6% | 36 lb | 2,160 sq ft | 4,320 sq ft |
| 12-12-12 | 12% | 40 lb | 4,800 sq ft | 9,600 sq ft |
Frequently Asked Questions
How much fertilizer do I need for my lawn?
It depends on your lawn size, the fertilizer's N%, and your target N rate. Formula: Product (lbs) = Area (sq ft) ÷ 1,000 × N rate (lbs/1,000 sq ft) ÷ (N% ÷ 100). Example: 5,000 sq ft lawn, 30-0-10 fertilizer (30% N), 1 lb N rate: Product = 5 × 1 ÷ 0.30 = 16.7 lbs. Our calculator does this instantly — enter your area and fertilizer above.
How much fertilizer per 1,000 square feet?
With a 30-0-10 fertilizer (30% N) at 1 lb N per 1,000 sq ft: 1 ÷ 0.30 = 3.33 lbs product per 1,000 sq ft. With 16-4-8 (16% N) at 1 lb N: 1 ÷ 0.16 = 6.25 lbs per 1,000 sq ft. The lower the N%, the more product you need. Never exceed 1 lb actual N per 1,000 sq ft per application.
What is the fertilizer calculation formula for lawns?
Product needed (lbs/1,000 sq ft) = N rate (lbs) ÷ N% (decimal). Total product (lbs) = Rate × Area ÷ 1,000. Bags = Total ÷ bag weight (round up). For 10,000 sq ft at 1 lb N/1,000 sqft using 30-0-10: Rate = 1÷0.30 = 3.33 lbs/1,000; Total = 3.33 × 10 = 33.3 lbs; Bags (40 lb bag) = ⌈33.3/40⌉ = 1 bag.
How much 20-10-10 fertilizer per acre?
1 acre = 43,560 sq ft = 43.56 units of 1,000 sq ft. At 1 lb N per 1,000 sq ft: Product = 1 ÷ 0.20 = 5 lbs/1,000 sqft. Total per acre = 5 × 43.56 = 217.8 lbs/acre. At a lighter 0.5 lb N rate: 108.9 lbs/acre. The calculator handles acres directly — select 'Acre' in the unit dropdown.
How often should I fertilize my lawn?
Cool-season grasses (fescue, bluegrass, ryegrass): 3-4 times/year — early spring (Mar-Apr), late spring (May), early fall (Sep), late fall (Nov). Skip summer. Warm-season grasses (bermuda, zoysia, St. Augustine): 3-5 times during growing season (May-Sep). Never fertilize warm-season grass in fall — it reduces winter hardiness.
What is the best fertilizer for lawns?
Depends on your goal: Quick green-up → 32-0-6 or 30-0-10 (high N, fast release). Balanced season feeding → 16-4-8 or 12-12-12. Slow-release organic → Milorganite 6-4-0 (safe, won't burn). High potassium for stress/drought → 15-0-15. Budget N source → 46-0-0 Urea. Always do a soil test first — if P is adequate, use N-only fertilizers.
What does 30-0-10 fertilizer mean?
30-0-10 means 30% Nitrogen (N), 0% Phosphorus (P₂O₅), 10% Potassium (K₂O) by weight. A 40 lb bag contains 40×0.30 = 12 lbs N and 40×0.10 = 4 lbs K. At 1 lb N per 1,000 sq ft, one 40 lb bag covers 12,000 sq ft. At 0.5 lb N rate, it covers 24,000 sq ft.
Can I over-fertilize my lawn?
Yes — over-fertilizing causes fertilizer burn (brown streaks), excessive thatch buildup, nutrient runoff into waterways, and wasted money. Max safe rate is 1 lb actual N per 1,000 sq ft per application. Slow-release fertilizers (organic or polymer-coated) are more forgiving. Water immediately after applying granular fertilizer to prevent leaf burn.