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This lawn fertilizer calculator tells you how much fertilizer product to spread to apply a chosen amount of nitrogen. Enter the three numbers from the bag (N-P-K), your lawn area and the nitrogen rate, and it calculates pounds per 1,000 square feet, total pounds and bags.
How to Use the Fertilizer Calculator
- Enter the lawn area in square feet.
- Enter the N-P-K numbers printed on the bag (for example 24-0-11).
- Enter how much nitrogen to apply per 1,000 sq ft.
- Enter the bag weight.
Fertilizer Formula
Product per 1,000 sq ft = Nitrogen rate ÷ (Nitrogen % ÷ 100)
The first number on the bag is the percentage of nitrogen by weight. A 24-0-11 fertilizer is 24% nitrogen, so 1 lb of nitrogen is in 1 ÷ 0.24 = 4.17 lb of product.
Example
To apply 1 lb of nitrogen per 1,000 sq ft on a 5,000 sq ft lawn with 24-0-11, spread 4.17 lb per 1,000 sq ft: 20.8 lb in total, a little more than one 15 lb bag. It also supplies 2.3 lb of potash.
Understanding N-P-K
| Number | Nutrient | What it does |
|---|---|---|
| First (N) | Nitrogen | Green color and leaf growth |
| Second (P) | Phosphate (P₂O₅) | Root growth, important for new lawns |
| Third (K) | Potash (K₂O) | Stress, drought and disease tolerance |
Lawn Fertilizing Tips
- Apply no more than about 1 lb of nitrogen per 1,000 sq ft at a time unless the label says otherwise.
- Fertilize cool-season grasses mainly in fall and warm-season grasses in late spring and summer.
- Keep granules off driveways and sidewalks and sweep them back onto the lawn.
- Follow local rules; some areas restrict phosphorus or limit application dates.
- A soil test tells you which nutrients your lawn actually needs.
Frequently Asked Questions
How much fertilizer do I need per 1,000 square feet?
Divide the nitrogen rate by the nitrogen percentage. For 1 lb of nitrogen with a 20-0-0 product, you need 5 lb per 1,000 sq ft.
What do the three numbers on fertilizer mean?
They are the percentages by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O).
How much 10-10-10 per 1,000 square feet?
To apply 1 lb of nitrogen, spread 10 lb of 10-10-10 per 1,000 sq ft.
Can I put down too much fertilizer?
Yes. Excess nitrogen can burn grass, encourage disease and wash into waterways.
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