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Fertilizer Calculator Guide
Lawn fertilizer is dosed by pounds of nitrogen per 1,000 square feet — not by the weight of the bag. This calculator converts your target nitrogen rate and your fertilizer's nitrogen percentage into the exact pounds of product to spread.
Product per 1,000 ft² = target N ÷ (N% ÷ 100). Multiply by (lawn area ÷ 1,000) for the total. To apply 1 lb of N with a 20% fertilizer: 1 ÷ 0.20 = 5 lbs of product per 1,000 sq ft.
How Much Fertilizer Do I Need?
Read the first number of the N-P-K on the bag (that's the nitrogen percentage). Divide your target nitrogen rate — usually 1 lb per 1,000 sq ft — by that percentage as a decimal to get pounds of product per 1,000 sq ft, then scale to your lawn's area.
Product Needed to Apply 1 lb of Nitrogen per 1,000 ft²
| Fertilizer N% | Pounds of product / 1,000 ft² |
|---|---|
| 10% | 10.0 lbs |
| 15% | 6.7 lbs |
| 20% | 5.0 lbs |
| 25% | 4.0 lbs |
| 30% | 3.3 lbs |
Worked Example
A 50 ft × 40 ft lawn = 2,000 sq ft. With a 20% nitrogen fertilizer at 1 lb N per 1,000 sq ft: product per 1,000 = 1 ÷ 0.20 = 5 lbs; total = 5 × (2,000 ÷ 1,000) = 10 lbs of fertilizer.
Tips
- Never exceed ~1 lb of N per 1,000 sq ft per application — more can burn the lawn. Split heavier feeding into multiple passes.
- Water it in after spreading (unless the label says otherwise) to move nutrients to the roots.
- Use a slow-release nitrogen for longer, more even feeding and less burn risk.
Seeding a new lawn too? See our Grass Seed Calculator, and top your beds with our Mulch Calculator.
Frequently Asked Questions
How much fertilizer do I need?
Divide your target nitrogen rate by the fertilizer's nitrogen percentage as a decimal, then multiply by your lawn area divided by 1,000.
How much nitrogen per 1,000 square feet?
1 pound of nitrogen per 1,000 square feet per application is the standard rate for most lawns.
How do I read the N-P-K ratio?
The three numbers are the percentages of nitrogen, phosphorus and potassium by weight — the first number is the nitrogen you dose by.
How much fertilizer to apply 1 pound of nitrogen?
Divide 1 by the nitrogen percentage as a decimal — a 20% fertilizer needs 5 pounds of product per 1,000 square feet.
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