Lawn Fertilizer Calculator
Calculate how many pounds and bags of fertilizer your lawn needs based on area, N-P-K analysis, and nitrogen target rate. Includes seasonal program planning and liquid vs granular comparison.
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How to Use This Calculator
Enter your lawn area in square feet, the N% from the fertilizer bag (first number in N-P-K), and your nitrogen target (default 1 lb N per 1,000 sq ft). Results show total pounds needed and bags to buy. Use Seasonal Plan to map out spring/summer/fall applications. Use the Professional tab with soil test values to calculate exactly how much N you still need to add.
Formula
Fertilizer needed = (N target lbs/1000 sq ft) ÷ (N% ÷ 100) × (area ÷ 1000)
Example: 1 lb N/1000 sqft ÷ 0.10 = 10 lbs fertilizer per 1000 sqft
Example
5,000 sq ft lawn, 10-10-10 fertilizer, 1 lb N/1000 sq ft target: 1 ÷ 0.10 = 10 lbs/1000 sq ft × 5 = 50 lbs total = 1 bag of 50 lbs
Frequently Asked Questions
- Divide your target nitrogen rate (lbs N per 1,000 sq ft) by the N percentage on the bag (as a decimal). For example, to apply 1 lb N/1,000 sq ft with a 10-10-10 fertilizer: 1 ÷ 0.10 = 10 lbs of fertilizer per 1,000 sq ft.
- N-P-K stands for Nitrogen-Phosphorus-Potassium. A bag labeled 10-10-10 contains 10% of each by weight. Nitrogen promotes leaf growth, phosphorus supports roots, and potassium improves stress resistance.
- Most lawns need 0.5–1.5 lbs of nitrogen per 1,000 sq ft per application. Cool-season grasses (fescue, bluegrass) do well with 1–1.5 lbs in fall and spring. Warm-season grasses (Bermuda, zoysia) need more in summer, typically 1–2 lbs.
- The general seasonal program: Spring (heavy, 1.5 lb N/1000 sq ft) to kick off growth, Summer (light, 0.5 lb N/1000 sq ft) to avoid burn, Fall (medium, 1.0 lb N/1000 sq ft) to strengthen roots before winter. Skip winter applications.
- Slow-release fertilizers (coated urea, sulfur-coated, polymer-coated) release nitrogen gradually over weeks. They reduce burn risk, require fewer applications, and feed more evenly. Aim for at least 30–50% slow-release content for best results.