Utility
Lawn Fertilizer Calculator
Calculate exactly how much fertilizer you need based on lawn area, grass type, N-P-K ratio, and your desired application rate.
Enter your lawn details and click Calculate
How is this calculated?
Total N needed = (Lawn Area ÷ 1000) × Application Rate
Product needed = Total N needed ÷ (N% ÷ 100)
Bags needed = Product needed ÷ Bag size (typically 25 or 50 lbs)
Example: 5000 sq ft, 20-5-10, 1 lb N/1000 sq ft
Total N = (5000 ÷ 1000) × 1 = 5 lbs N
Product = 5 ÷ 0.20 = 25 lbs fertilizer
Bags (50 lb) = 25 ÷ 50 = 0.5 bags = 1 bag
Annual applications:
Cool season: 3-4 per year (Sept, Nov, Apr, Jun)
Warm season: 4-5 per year (Apr-Sep monthly)FAQ
Frequently asked questions about lawn fertilizer
How much fertilizer do I need per 1000 sq ft?
Most lawns need 1 lb of nitrogen per 1000 sq ft per application. For a 10-10-10 fertilizer (10% N), you'd need 10 lbs of product per 1000 sq ft to deliver 1 lb of actual nitrogen.
What does N-P-K mean on fertilizer?
N-P-K stands for Nitrogen-Phosphorus-Potassium, the three primary plant nutrients. The numbers represent the percentage by weight: 20-5-10 means 20% nitrogen, 5% phosphorus, 10% potassium. Nitrogen promotes leaf growth, phosphorus supports roots, potassium aids stress resistance.
When should I fertilize my lawn?
Cool-season grasses (fescue, bluegrass): fertilize in early fall and late spring. Warm-season grasses (bermuda, zoysia): fertilize in late spring through summer. Avoid fertilizing during extreme heat or drought.
Can you over-fertilize a lawn?
Yes, over-fertilizing causes 'fertilizer burn' with brown/yellow patches, excessive growth requiring more mowing, thatch buildup, and nutrient runoff harming waterways. Always follow recommended rates and water after application.
What's the best fertilizer ratio for lawns?
For general maintenance: 3-1-2 or 4-1-2 ratio (e.g., 24-8-16). For new lawns: higher phosphorus like 10-18-10. For fall feeding: lower nitrogen, higher potassium like 10-0-20. Soil tests reveal exactly what your lawn needs.
Should I water after fertilizing?
Yes, water lightly (about 0.25 inches) within 24 hours of applying granular fertilizer to wash it off grass blades and into the soil. Don't over-water or you'll wash nutrients away. Liquid fertilizer is absorbed faster.