Lawn fertilizer calculator
Use the first number on the fertilizer bag and your lawn size to find how many pounds of product to spread and how many bags to buy.
Estimates round up. Check product labels and supplier figures before ordering.
Pounds of product per 1,000 sq ft
| Product (N-P-K) | Nitrogen | Product for 1 lb N per 1,000 sq ft |
|---|---|---|
| 10-10-10 | 10% | 10 lb |
| 16-4-8 | 16% | 6.25 lb |
| 20-0-5 | 20% | 5 lb |
| 24-0-11 | 24% | 4.2 lb |
| 29-0-4 | 29% | 3.4 lb |
| 32-0-4 | 32% | 3.1 lb |
How it's calculated
Lawn fertilizer rates are given as pounds of nitrogen per 1,000 square feet, not pounds of product. The first number in the N-P-K is the percent of the bag's weight that is nitrogen, so the calculator divides your target rate by that percent.
Product per 1,000 sq ft = target lb N / (N% / 100)
Total product = product per 1,000 sq ft x area (sq ft) / 1,000
Bags = total product / bag weight
Example: a 32-0-4 product at 1 lb N per 1,000 sq ft needs 1 / 0.32 = 3.125 lb of product per 1,000 sq ft. A 5,625 sq ft lawn takes about 17.6 lb, which is one 20 lb bag.
University extension guides usually suggest 0.5 to 1 lb of nitrogen per feeding, with no more than about 0.5 lb from fast-release products. Total yearly nitrogen depends on grass type and region. Always follow the product label and any local fertilizer rules, which take priority over this estimate.
What you'll need
- Lawn fertilizer
- Broadcast spreader
- Soil test kit
- Drop spreader
Common questions
How do I read the numbers on a fertilizer bag?
The three numbers are the percent by weight of nitrogen, phosphate and potash. A 50 lb bag of 20-5-10 contains 10 lb of nitrogen.
How much fertilizer per 1,000 square feet?
Divide your target nitrogen rate by the nitrogen percent. For 1 lb of nitrogen from a 20-0-5 product that is 5 lb of product per 1,000 square feet.
How much nitrogen should I put on my lawn per year?
Often 2 to 4 lb per 1,000 square feet a year for cool-season lawns, split across several feedings. Warm-season grasses and low-input lawns vary, so check your local extension guide.
Should I water in fertilizer?
Most granular lawn fertilizers should be watered in with about 1/4 inch of water soon after applying, but follow the label, since some weed-and-feed products need dry leaves.