Lawn
Fertilizer Calculator
Enter the first number from the bag and the nitrogen rate you want. This works backwards to the pounds of product you actually spread.
The first number on the bag is the percentage of nitrogen.
Pounds of actual nitrogen per 1,000 ft². One pound is a standard single application.
Pounds per bag.
Quantity estimate for planning and buying. Rates vary by variety, region and product — check the label on what you actually buy.
The calculation almost nobody does
Lawn fertilizer is applied by nitrogen, not by product. The standard single application is 1 lb of actual nitrogen per 1,000 ft², and how much product that means depends entirely on the analysis on the bag.
lb of product per 1,000 ft² = target lb N × 100 ÷ N%
So for a 24-0-4 product: 1 × 100 ÷ 24 = 4.17 lb of product per 1,000 ft². For a 10-10-10: 1 × 100 ÷ 10 = 10 lb. Same nitrogen, two and a half times the product. Spreading 10 lb of the 24-0-4 because that is what the 10-10-10 needed puts down 2.4 lb of nitrogen, which will burn the lawn.
What the three numbers mean
N-P-K, always in that order, always percentages by weight: nitrogen for leaf and colour growth, phosphorus for roots and establishment, potassium for stress and disease tolerance.
A 50 lb bag of 24-0-4 contains 12 lb of nitrogen, no phosphorus, and 2 lb of potassium. The other 36 lb is carrier — which is why cheap fertilizer is not always cheap per pound of nutrient, and why comparing bag prices without doing this arithmetic is meaningless.
Many US states restrict or ban phosphorus in lawn fertilizer because of runoff into waterways, which is why so many lawn products now show a zero in the middle. Unless a soil test says you need phosphorus, you almost certainly do not.
| Analysis | Nitrogen | lb product per 1,000 ft² | A 15 lb bag covers |
|---|---|---|---|
| 24-0-4 | 24% | 4.17 lb | 3,600 ft² |
| 29-0-4 | 29% | 3.45 lb | 4,350 ft² |
| 32-0-4 | 32% | 3.13 lb | 4,800 ft² |
| 20-20-20 | 20% | 5.00 lb | 3,000 ft² |
| 16-4-8 | 16% | 6.25 lb | 2,400 ft² |
| 10-10-10 | 10% | 10.00 lb | 1,500 ft² |
| 12-4-8 | 12% | 8.33 lb | 1,800 ft² |
| 5-10-5 | 5% | 20.00 lb | 750 ft² |
How much nitrogen per year
A single application is 1 lb N per 1,000 ft², and never more than that at once from a quick-release product. The annual budget depends on the grass and how hard you push it:
| Lawn type | Nitrogen per year | Applications |
|---|---|---|
| Cool-season, low maintenance | 1-2 lb | 1-2 applications |
| Cool-season, standard | 2-4 lb | 3-4 applications |
| Warm-season, standard | 2-4 lb | 3-4 applications |
| Bermudagrass, high maintenance | 4-6 lb | 4-6 applications |
| Centipede (low feeder) | 0.5-1 lb | 1 application |
Practical notes
- Calibrate the spreader. The setting numbers on a spreader dial are not units. Weigh out the product for a known area, spread it, and adjust.
- Half rate, two passes, at right angles. Far more even than one pass at full rate, and it hides the stripes.
- Water it in unless it is a slow-release granular going onto damp soil.
- Sweep hard surfaces back onto the lawn. Fertilizer on a driveway goes straight into the storm drain.
- Do not feed dormant or drought-stressed grass. You are paying to stress it further.
Common questions
How much fertilizer do I need per 1,000 square feet?
Divide 100 by the first number on the bag. A 24-0-4 needs 4.17 lb of product to deliver 1 lb of nitrogen per 1,000 ft²; a 10-10-10 needs 10 lb; a 32-0-4 needs 3.13 lb.
What do the three numbers on fertilizer mean?
Percentages by weight of nitrogen, phosphorus and potassium, in that order. A 50 lb bag of 24-0-4 holds 12 lb of nitrogen, no phosphorus and 2 lb of potassium.
How much fertilizer for a 5,000 square foot lawn?
With a 24-0-4 product at the standard 1 lb N rate, 20.8 lb of product — so two 15 lb bags. The same lawn with 10-10-10 would need 50 lb.
Can I put down too much fertilizer?
Yes, and it burns the grass. Never exceed 1 lb of nitrogen per 1,000 ft² in one application from a quick-release product. The damage shows as yellow or brown stripes following your spreader pattern.