Fertilizer Needed
0 lbs
Bags Needed
0
Total Cost
$0.00
| Item | Value |
|---|---|
| Area | 0 sq ft |
| Target N | 1.0 lbs/1000 sq ft |
| Fertilizer N-P-K | 10-10-10 |
| Application Rate | 0 lbs/1000 sq ft |
| Total Needed | 0 lbs |
| Bags | 0 |
| Cost | $0.00 |
Fertilizer Calculator: How Much N-P-K Do You Really Need in 2025?
Stop guessing and start growing smarter. Our fertilizer calculator uses soil test results, area, and NPK ratio to give you exact granular or liquid amounts, cost, and schedule.
How the Fertilizer Calculator Works
Formula:
- Area (sq ft) = Length × Width
- Target N (lbs) = (Area ÷ 1000) × Target N per 1000 sq ft
- Fertilizer Needed = Target N ÷ (N% ÷ 100)
- Bags = Ceiling(Fertilizer Needed ÷ Bag Size)
Example: 50×20 ft Lawn, 10-10-10, 1 lb N/1000 sq ft, 50 lb bag
- Area: 1,000 sq ft
- Target N: 1 lb
- Fertilizer: 1 ÷ 0.10 = 10 lbs
- Bags: 10 ÷ 50 = 0.2 → buy 1
Common N-P-K Ratios
| Ratio | Use |
|---|---|
| 10-10-10 | All-purpose, lawns, vegetables |
| 16-4-8 | Lawn starter |
| 5-10-5 | Flowers, shrubs |
| 0-0-50 | Potash boost |
| 20-0-0 | Nitrogen only |
Application Rates by Plant
| Plant | N lbs/1000 sq ft | Frequency |
|---|---|---|
| Lawn (cool-season) | 1.0–1.5 | Every 6–8 weeks |
| Lawn (warm-season) | 0.5–1.0 | Every 4–6 weeks |
| Vegetables | 0.1–0.2 per plant | At transplant + 3 weeks |
| Roses | 0.5–1.0 | Spring + midsummer |
Granular vs Liquid
- Granular: Slow-release, 4–8 weeks
- Liquid: Fast-acting, 1–2 weeks
- Granular: Better for large areas
- Liquid: Precise for containers
Soil Test Interpretation
- Nitrogen (N): Rarely tested — use growth
- Phosphorus (P): >50 ppm = none needed
- Potassium (K): >150 ppm = none needed
- pH: 6.0–7.0 ideal
Pro Tips
- Apply early morning or evening
- Water in ½ inch after granular
- Never fertilize dry soil
- Use drop spreader for even coverage
- Sweep granules off sidewalks
Seasonal Schedule
- Spring: High-N for growth
- Summer: Balanced, stress relief
- Fall: High-K for roots
- Winter: None (dormant)
Cost Example
| Item | Qty | Price | Total |
|---|---|---|---|
| Fertilizer (1 bag) | 1 | $25 | $25 |
| Spreader rental | — | — | $15 |
| Total | — | — | $40 |
Related Calculators
FAQs
How often to fertilize lawn? 4–6 times per year.
Can I mix fertilizers? Only if compatible.
Is organic better? Slower release, soil health.
What if I over-fertilize? Burn, runoff — flush with water.
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