Lawn Fertilizer & Spreader Rate Calculator (N-P-K)
Calculate exact fertilizer pounds, nitrogen rates per 1,000 sq ft, N-P-K ratios, and broadcast spreader calibration settings.
Calculated Results
Frequently Asked Questions
What do the three numbers (N-P-K) on a fertilizer bag mean?
The three numbers represent the guaranteed percentage by weight of the three primary macronutrients: N (Nitrogen - stimulates green foliage growth), P (Phosphorus as P₂O₅ - promotes root development), and K (Potassium as K₂O - builds disease resistance and drought tolerance). A 50-lb bag of 32-0-4 contains 32% Nitrogen (16 lbs pure N), 0% Phosphorus, and 4% Potassium (2 lbs K).
How do you calculate how many pounds of fertilizer you need per 1,000 sq ft?
Formula: Pounds of Fertilizer = (Desired lbs of Nitrogen) / (Percentage of Nitrogen / 100). For 1.0 lb of N using a 32-0-4 fertilizer: 1.0 / 0.32 = 3.125 lbs of fertilizer per 1,000 sq ft.
Why should you avoid over-fertilizing your lawn?
Applying more than 1.0 to 1.5 lbs of fast-release nitrogen per 1,000 sq ft causes chemical 'fertilizer burn' (desiccating grass roots via osmotic shock) and leads to nutrient runoff that pollutes groundwater and streams.
What is the difference between a broadcast rotary spreader and a drop spreader?
A broadcast rotary spreader flings fertilizer granules in a wide 6-to-12-foot semi-circle, making it much faster for large open yards. A drop spreader drops granules directly between its wheels with precise edges, ideal for narrow strips near gardens, driveways, and sidewalks.