🧪 Fertilizer Calculator (Nitrogen Rate)
Enter your target nitrogen rate, your area and the fertilizer's %N, and get how much product to apply.
Fertilizer to apply
10 lb
4.54 kg
Actual N delivered
2 lb
Rate
24 g/m²
Product needed = (target lb N per 1,000 ft² × area ÷ 1,000) ÷ (%N ÷ 100). The %N is the first number in the N-P-K analysis (e.g. 20 in 20-5-10). A typical lawn rate is about 1 lb N per 1,000 ft² per feeding — don't over-apply. 🔒 In your browser.
How the fertilizer calculator (nitrogen rate) works
Fertilizer is dosed by the nutrient it delivers, not the bag weight. The amount of product is the target nitrogen (in pounds per 1,000 ft²) times your area, divided by the fraction of nitrogen in the fertilizer: lb product = (target lb N per 1,000 ft² × area ÷ 1,000) ÷ (%N ÷ 100). The %N is the first number in the N-P-K analysis on the label.
A typical lawn feeding is about 1 lb of nitrogen per 1,000 ft² per application — the seasonal total is spread across several feedings. More is not better: over-applying nitrogen burns plants, wastes money and pollutes waterways through runoff. Water in granular fertilizer after applying.
Frequently asked questions
How much fertilizer do I need?
Product needed = (target lb N per 1,000 ft² × area ÷ 1,000) ÷ (%N ÷ 100). For 1 lb N over 2,000 ft² with a 20-5-10 fertilizer: (1 × 2) ÷ 0.20 = 10 lb of product.
What do the N-P-K numbers mean?
They're the percentages by weight of nitrogen (N), phosphorus (P₂O₅) and potassium (K₂O). A 20-5-10 bag is 20% nitrogen. This calculator uses the first number, %N, since nitrogen usually drives the application rate.
How much nitrogen should I apply to a lawn?
About 1 lb of actual nitrogen per 1,000 ft² per application is a common guideline, with the yearly total split across several feedings depending on grass type and climate. Follow local extension recommendations.
Can I apply too much fertilizer?
Yes. Excess nitrogen scorches foliage, promotes weak leafy growth, wastes money and runs off into waterways causing pollution. Measure to a target rate rather than guessing, and don't exceed label rates.
How do I convert the rate to a smaller area?
The formula scales with area — the tool divides your area by 1,000 automatically. For a 250 ft² bed at 1 lb N/1,000 ft² with 10% N, that's (1 × 0.25) ÷ 0.10 = 2.5 lb of product.