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Fertilizer NPK Calculator
Calculate exact Nitrogen (N), Phosphorus (P2O5), and Potassium (K2O) nutrient amounts and application weights per square foot or acre from target NPK ratios.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Total Fertilizer Product Needed
Application Rate per 1,000 sq ft
Delivered Nutrient Mass Breakdown
| Nutrient Component | Blend % | Total Delivered Weight (lbs) | Rate per 1,000 sq ft |
|---|
How it works
- Enter the three N-P-K grade percentages from your fertilizer bag (e.g. 10-10-10 or 24-0-4).
- Specify your target Nitrogen application rate per 1,000 square feet (typically 0.75 to 1.0 lb).
- Enter your total lawn, turf, or garden area.
- The calculator determines total product weight required and the exact pounds of elemental Nitrogen, Phosphate, and Potash delivered.
The formula
Fertilizer Weight per 1,000 sq ft = Target Nitrogen Rate (lbs) / (N % / 100)
Total Fertilizer Required (lbs) = (Fertilizer per 1,000 sq ft) × (Total Area in sq ft / 1000)
FAQ
What do the three numbers on a fertilizer bag mean (NPK)?
The three numbers represent the guaranteed minimum percentage by weight of Nitrogen (N), available Phosphate (P₂O₅), and soluble Potash (K₂O). For example, a 50 lb bag of 10-10-10 contains 10% (5 lbs) Nitrogen, 10% (5 lbs) Phosphate, and 10% (5 lbs) Potash.
What is the standard lawn nitrogen application rate?
Most turfgrass extension guidelines recommend applying 0.75 to 1.0 lb of actual nitrogen per 1,000 square feet per application during active growing seasons to promote healthy root growth without scorching.
How do you calculate how many bags of fertilizer to purchase?
Divide the total required fertilizer weight (in lbs) by the net weight of a commercial bag (commonly 20, 25, 40, or 50 lbs) and round up to the nearest whole bag.
Can I use this calculator for garden beds and agricultural acreage?
Yes. You can switch between square feet, square meters, and acres to determine exact bulk application tonnages or garden spreader settings.
How we compare
| Feature | Online Tool Store | Lawn care brand calculators | Manual formula |
|---|---|---|---|
| Custom N-P-K grade ratios | ✓ | Locked to single brand | ✓ |
| Elemental phosphate & potash yield breakdown | ✓ | ✗ | ✗ |
| Multi-unit area support (Acre, sq ft, m²) | ✓ | Partial | ✗ |