How much fertilizer do I need for my lawn?
Short answer: pounds of product per 1,000 sq ft = target pounds of nitrogen ÷ (N% ÷ 100). For 1 lb of nitrogen from a 24-0-11 bag, that is 1 ÷ 0.24 = 4.17 lb per 1,000 sq ft, or about 20.8 lb for a 5,000 sq ft lawn. Enter your own lawn and bag below.
Not sure when to feed? See when to fertilize your lawn, by grass type.
1. Your lawn and your bag
1 lb is the most quick-release nitrogen Purdue and Texas A&M advise per feeding. Purdue uses 0.5 to 0.75 lb for late-fall feedings. In Florida, UF/IFAS caps quick-release nitrogen at 0.7 lb, so pick 0.5 unless the bag is mostly slow-release.
The three numbers on the bag are percentages by weight. Only the first one, nitrogen, sets the rate.
2. How much to spread
- Per 1,000 sq ft
- 4.17 lb
- For your lawn
- 20.8 lb
- Bags to buy
- 1
of product for 1 lb of nitrogen
5,000 sq ft
40 lb bags, rounded up. One bag covers about 9,600 sq ft at this rate.
This feeding also delivers 0 lb of phosphate (P2O5) and 0.46 lb of potash (K2O) per 1,000 sq ft. That is 0 lb and 2.29 lb across your lawn.
How this is calculated
- Product per 1,000 sq ft = target lb of nitrogen ÷ (N% ÷ 100).
- Total product = product per 1,000 sq ft × lawn sq ft ÷ 1,000.
- Bags = total ÷ bag weight, rounded up. Area per bag = bag weight ÷ product per 1,000 sq ft × 1,000.
- Phosphate and potash = product weight × the second or third bag number ÷ 100.
- Set your spreader by the bag's directions, then check that it puts down roughly this amount.
How the bag numbers work
The three numbers on a fertilizer bag (N-P-K) are percentages by weight. The first is nitrogen. The second is phosphate (P2O5) and the third is potash (K2O). Lawn rates are set by nitrogen, so the first number decides how much product you spread.
Texas A&M AgriLife shows the reverse check: multiply bag weight by N%. A 40 lb bag of 16-4-8 holds 40 × 0.16 = 6.4 lb of nitrogen. At 1 lb per 1,000 sq ft, it treats 6,400 sq ft.
Worked example: 24-0-11 on 5,000 sq ft
- Product per 1,000 sq ft: 1 ÷ 0.24 = 4.17 lb.
- Total for the lawn: 4.17 × 5 = 20.8 lb.
- With a 40 lb bag: one bag is enough, and it covers about 9,600 sq ft at this rate.
- Potash delivered: 20.8 × 0.11 = 2.3 lb of K2O, or 0.46 lb per 1,000 sq ft. No phosphate, since the middle number is 0.
Pounds of product per 1,000 sq ft for common bags
| Bag N-P-K | For 0.5 lb N | For 0.75 lb N | For 1 lb N |
|---|---|---|---|
| 16-4-8 | 3.1 lb | 4.7 lb | 6.25 lb |
| 21-0-0 | 2.4 lb | 3.6 lb | 4.8 lb |
| 24-0-11 | 2.1 lb | 3.1 lb | 4.2 lb |
| 29-0-4 | 1.7 lb | 2.6 lb | 3.4 lb |
| 46-0-0 | 1.1 lb | 1.6 lb | 2.2 lb |
Clemson HGIC gives the same math for 21-0-0 (ammonium sulfate): about 4.75 lb supplies 1 lb of nitrogen per 1,000 sq ft.
How much nitrogen per feeding
- Standard: Purdue Extension caps quick-release nitrogen at 1 lb per 1,000 sq ft per application. Texas A&M also recommends 1 lb or less, 45 to 60 days apart.
- Mostly slow-release bags: Purdue allows up to 2 lb per application when more than half the nitrogen is slow-release.
- Florida: UF/IFAS limits quick-release nitrogen to 0.7 lb per application. Slow-release can go to 2 lb in spring and summer, but only 1 lb in fall and winter.
Spread it safely
- Sweep up strays. Purdue says to clean fertilizer off sidewalks, driveways and roads, using a broom or blower to return it to the grass.
- Skip frozen or dormant lawns. Purdue advises no fertilizer in winter or on frozen soil, and none on dormant or severely drought-stressed turf.
- Water in quick-release nitrogen. Purdue and Clemson both advise watering after application to reduce leaf burn.
- Don't overdo it. Purdue warns that excess fertilizer contaminates surface water and groundwater. UF/IFAS notes extra phosphorus can enrich runoff.
Common questions
How much 24-0-11 do I need per 1,000 sq ft?
About 4.2 lb gives 1 lb of nitrogen, because 1 ÷ 0.24 = 4.17. For a lighter 0.5 lb feeding, use about 2.1 lb.
How many square feet does a bag cover?
Multiply bag weight by N% to get pounds of nitrogen, then multiply by 1,000. A 40 lb bag of 16-4-8 covers 6,400 sq ft at 1 lb N.
Do the second and third numbers change the amount?
No. Rates are based on nitrogen. Phosphate and potash just come along with it, which the calculator shows as a note.
Should I get a soil test first?
Yes. UF/IFAS and Texas A&M both recommend one. It shows whether your lawn needs phosphorus or potassium at all.