Fertilizer Calculator
Find how much fertilizer to spread on your lawn from its size, your target nitrogen rate, and the nitrogen percentage on the bag.
What your result means
Fertilizer to apply is the total pounds of product to spread to hit your nitrogen target. Actual nitrogen is how much real N that delivers. The per-1,000 figure is the spreader rate. Lawns are fed by nitrogen, and the bag's first N-P-K number tells you how concentrated it is. Measure your lawn first with our square footage calculator.
How to use this calculator
- Measure your lawn area in square feet.
- Pick a target nitrogen rate — 0.5 to 1 lb of N per 1,000 sq ft per feeding.
- Read the fertilizer's nitrogen percentage (the first N-P-K number).
- Read the total pounds to apply and the spreader rate.
- Never exceed about 1 lb of actual N per 1,000 sq ft in one feeding.
The formula
To deliver a target amount of nitrogen, divide it by the fertilizer's nitrogen fraction to get product pounds per 1,000 sq ft, then scale to your lawn size. Only the N percentage matters for the nitrogen target.
Worked example
A 5,000 sq ft lawn fed at 1 lb of nitrogen per 1,000 sq ft using a 26-0-3 product needs 1 / 0.26 = 3.85 lbs of product per 1,000, or about 19.2 lbs total — delivering roughly 5 lbs of actual nitrogen.
Nitrogen rate guide
| Goal | N per 1,000 sq ft |
|---|---|
| Light / slow feeding | 0.5 lb |
| Standard feeding | 0.75 - 1 lb |
| Max single application | 1 lb (don't exceed) |
| Annual total (cool-season) | 2 - 4 lbs |
| Annual total (warm-season) | 3 - 5 lbs |
Tips & gotchas
- Don't exceed 1 lb of actual nitrogen per 1,000 sq ft in one feeding, or you risk burning the lawn.
- Slow-release nitrogen feeds longer and burns less than quick-release.
- Calibrate your spreader — settings vary by product granule size.
- Water in granular fertilizer (unless it's a weed-and-feed) to move it to the roots.
- Only the first N-P-K number drives the nitrogen math; P and K are separate goals.
Frequently asked questions
How much fertilizer do I need for my lawn?
Divide your target nitrogen rate by the fertilizer's N fraction, then scale to your lawn size. A 5,000 sq ft lawn at 1 lb N/1,000 with 26% N needs about 19 lbs of product.
What does the N-P-K number mean?
The three numbers are the percentages of nitrogen, phosphorus, and potassium. For lawn feeding, nitrogen (the first number) drives the application rate.
How much nitrogen is too much?
More than about 1 lb of actual nitrogen per 1,000 sq ft in a single feeding can burn the lawn. Spread the annual total across several applications.
How often should I fertilize?
Most lawns want 2 to 5 lbs of nitrogen per 1,000 sq ft per year, split into 3 to 5 feedings during the growing season.
Should I water after fertilizing?
Yes for granular products, to move nitrogen to the roots and reduce burn risk — unless it's a weed-and-feed that needs to stay on the leaves first.
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