How it works
The formula
total = area ÷ 1,000 × product per 1,000 sq ft
bags = total ÷ bag weight, rounded up
Assumptions
- Rate: about 1 lb of actual nitrogen per 1,000 sq ft per feeding, and no more than 1 lb of quick-release nitrogen at once (Purdue Extension, A Simple Procedure for Fertilizing Cool-Season Lawns; UConn, Suggested Fertilizer Practices for Lawns). Slow-release products may allow more; the label rules.
- Cool-season lawns need about 2 lb of nitrogen per 1,000 sq ft a year with clippings left on (UConn), split into feedings in late spring and early fall.
- The bag's three numbers are the percent nitrogen, phosphate and potash by weight. Only the first sets this rate.
Worked example
A 50 × 40 ft lawn with 32-0-4 fertilizer at 1 lb of nitrogen per 1,000 sq ft
- 1 ÷ 0.32 = 3.1 lb of product per 1,000 sq ft
- 2,000 ÷ 1,000 × 3.125 = 6.25 lb, so 1 bag of 12.5 lb (half of it)
Pounds per 1,000 sq ft for 1 lb of nitrogen
| Nitrogen % | lb per 1,000 sq ft |
|---|---|
| 10% | 10.0 |
| 16% | 6.3 |
| 21% | 4.8 |
| 24% | 4.2 |
| 29% | 3.4 |
| 32% | 3.1 |
| 46% | 2.2 |
Questions people ask
How much fertilizer per 1,000 sq ft?
Divide the nitrogen you want, usually 1 lb, by the bag's nitrogen percent: 3.1 lb of a 32-0-4 fertilizer, 4.8 lb of 21-0-0 or 10.0 lb of 10-10-10.
How many bags of fertilizer for my lawn?
A 12.5 lb bag of 32-0-4 covers about 5,000 sq ft at the label rate, about 0.8 lb of nitrogen per 1,000 sq ft. At the full 1 lb rate it covers 4,000 sq ft. Enter your lawn above for the exact count.
When should I fertilize?
For cool-season grass, late spring and early fall; UConn advises against fertilizing after mid-October or before mid-April. Warm-season grass is fed in late spring and summer while it grows.
What do the three numbers mean?
Nitrogen, phosphate and potash, as percent of the bag's weight. Many states limit phosphorus on lawns unless a soil test shows a need.