How much fertilizer do I need for my lawn?
Lawn fertilizer rates are set by nitrogen, not by the weight of the bag. The first number in the N-P-K on the label is the percent nitrogen by weight. Divide the nitrogen you want by that percent to get pounds of product.
Lb of product per 1,000 sq ft = lb of nitrogen per 1,000 sq ft ÷ (% N ÷ 100)
A 100 × 50 ft lawn is 5,000 sq ft. At 1 lb of nitrogen per 1,000 sq ft with a 24-0-6 fertilizer, you need 1 ÷ 0.24 = 4.17 lb of product per 1,000 sq ft, or 20.8 lb in total. One 50 lb bag covers it with plenty left over.
Always follow the label. It gives the maximum rate, spreader settings and any restrictions for your product, and it's the legal limit for how the product can be used.
Pounds of product for 1 lb of nitrogen
| Nitrogen (first number) | Lb of product per 1,000 sq ft | Lb per 5,000 sq ft |
|---|---|---|
| 10% | 10 | 50 |
| 16% | 6.25 | 31.3 |
| 20% | 5 | 25 |
| 24% | 4.17 | 20.8 |
| 29% | 3.45 | 17.2 |
| 32% | 3.13 | 15.6 |
| 46% (urea) | 2.17 | 10.9 |
Extension guides typically recommend no more than about 1 lb of quick-release nitrogen per 1,000 sq ft in one application. Yearly totals depend on the grass and your region, so check with your local extension office.
Lawn fertilizer calculator
Most bagged lawn fertilizer is granular. Retail bags often say how many square feet they cover, and that figure is usually based on about 1 lb of nitrogen or less per 1,000 sq ft. If you want a lighter feeding, set the nitrogen to 0.5 or 0.75 lb and the calculator gives the product amount and spreader rate to match.
Liquid fertilizer calculator
For liquids you need one more number: how much a gallon of the product weighs. It's on the label or the safety data sheet. A 28-0-0 UAN solution weighs about 10.65 lb per gallon, so a gallon holds about 2.98 lb of nitrogen.
Gallons of product = lb of nitrogen ÷ (% N ÷ 100) ÷ lb per gallon
For 5,000 sq ft at 0.5 lb of nitrogen per 1,000 sq ft with 28-0-0: 2.5 lb N ÷ 0.28 ÷ 10.65 = 0.84 gal, or 107 fl oz. That's 21.5 fl oz per 1,000 sq ft. At 1 gal of water per 1,000 sq ft, it goes out in about 5 gal of spray mix.
Liquid nitrogen can burn grass at high rates or in hot weather, which is why liquid feedings are often lighter. Follow the label for the rate and the spray volume.
Phosphorus and potassium
The second and third numbers are phosphate (P) and potash (K). Many established lawns need little or no phosphorus, and several states restrict phosphorus fertilizer on lawns unless a soil test shows a need. A soil test is the only reliable way to know what your lawn is short of.
Pricing a fertilizer application
Lawn care companies usually price fertilizer per application by lawn size, built from product at cost plus markup and time on site. Use contractor mode to add your markup and labor, then send it as a landscaping estimate. Your state may require a license to apply fertilizer or pesticides for hire.
Questions
How much fertilizer should I put on my lawn?
A common rate is 1 lb of nitrogen per 1,000 sq ft per application. Divide that by the percent nitrogen on the bag: with 24-0-6, that's about 4.2 lb of product per 1,000 sq ft. Follow the label's maximum.
What do the three numbers on fertilizer mean?
They're the percent by weight of nitrogen (N), phosphate (P2O5) and potash (K2O). A 50 lb bag of 24-0-6 holds 12 lb of nitrogen.
How much area does a 50 lb bag of fertilizer cover?
Divide the pounds of nitrogen in the bag by your rate. A 50 lb bag of 24-0-6 holds 12 lb of nitrogen, so at 1 lb per 1,000 sq ft it covers 12,000 sq ft.
How do I calculate liquid fertilizer?
Divide the pounds of nitrogen you need by the percent nitrogen, then by the product's weight per gallon. Multiply gallons by 128 for fluid ounces.