Fertilizer Rate Calculator
What is fertilizer analysis (N-P-K)?
The three numbers on a fertilizer bag are not elemental nutrients — they are oxide forms for phosphorus and potassium.
| Label | What it means |
|---|---|
| N | Elemental nitrogen (%) |
| P | Phosphorus as P₂O₅ (not elemental P) |
| K | Potassium as K₂O (not elemental K) |
Conversions:
- Elemental P = P₂O₅ × 0.44
- Elemental K = K₂O × 0.83
A recommendation for 40 lbs P₂O₅/acre is not 40 lbs of elemental phosphorus — it is 40 lbs of the oxide form your lab and Extension use. This calculator works in P₂O₅ and K₂O to match your recommendation sheet.
How to get a nutrient recommendation
This tool converts a recommendation to a product rate — it does not generate the recommendation from scratch.
- Soil test — sample correctly, send to a reputable lab
- Recommendation — from Extension, certified crop advisor, or agronomist (lbs N, P₂O₅, K₂O per acre)
- Product rate — use this calculator to convert to lbs urea, gallons UAN, lbs DAP, etc.
Start with the soil test interpretation guide to understand your test numbers before converting to application rates.
Common fertilizer products
| Product | Analysis | Form | Notes |
|---|---|---|---|
| Anhydrous ammonia | 82-0-0 | Gas | Highest N%; requires injector |
| Urea | 46-0-0 | Dry | Most common dry N |
| UAN 28% | 28-0-0 | Liquid | Common sidedress |
| UAN 32% | 32-0-0 | Liquid | Higher N%, less water |
| Ammonium sulfate | 21-0-0-24S | Dry | Adds sulfur; acidifying |
| DAP | 18-46-0 | Dry | Common starter P |
| MAP | 11-52-0 | Dry | Higher P than DAP |
| Triple superphosphate | 0-46-0 | Dry | No N |
| Muriate of potash | 0-0-60 | Dry | Standard K source |
Pair your fertility cost with the crop breakeven calculator to know what your nutrient investment needs to return. For CEC and base saturation context, see the CEC calculator.
Fertilizer Rate Calculator FAQ
How do I know how much fertilizer to apply per acre?
Get a soil test recommendation first, then convert lbs nutrient to lbs product with this calculator.
What is the difference between DAP and MAP?
DAP has more N (18%); MAP has more P (52% P₂O₅). Pick based on which nutrient you need.
How do I convert lbs of nutrient to lbs of product?
Divide lbs nutrient by the fraction in the product (e.g. 120 N ÷ 0.46 = 261 lbs urea).
What is ECCE for lime?
Effective Calcium Carbonate Equivalent — neutralizing power of your lime vs. pure calcium carbonate.
Can I use this calculator for liquid fertilizer?
Yes — UAN products show gal/acre and lbs/acre.