Fertilizer Calculator
Turn nutrient targets into a precise fertilizer plan.
Label grade = % N – % P₂O₅ – % K₂O. Custom values can be entered below.
Area, Targets & Fertilizer
Result & Nutrient Review
Nutrient Target Coverage
Coverage compares label nutrients with entered application targets.
Bagging & Purchase Plan
500 kg purchased − 480 kg applied = 20 kg remaining
If a selected fertilizer has 0% of the basis nutrient, choose another basis or product.
Nutrient Supply & Balance
| Nutrient | Target (kg/ha) | Supplied (kg/ha) | Total supplied (kg) | Balance (kg) |
|---|
Targets are illustrative, not a fertilizer recommendation. Other label nutrients may be below or above target when you change the dose basis.
Understanding your application
Product mass = target nutrient mass ÷ label fraction
Example (N-based): 0.80 ha × 120 kg N/ha ÷ 0.20 = 480 kg
One fertilizer may not satisfy all three targets. Review each surplus or deficit.
Application basis & limitations
Enter crop- and site-specific recommended application rates, not soil concentrations. This calculator does not infer a nutrient recommendation from ppm, soil mass, crop yield or a generic “safe” dose. The label grade is N–P₂O₅–K₂O, not elemental N–P–K; targets must use the same basis.
Positive balance means more label nutrient than the net target; negative means a shortfall. Blank secondary targets are unknown, not zero. A zero target with positive supply is an excess. Credits only reduce the remaining application target when explicitly enabled. Follow product directions, local restrictions and your agronomist’s advice.
A target match is arithmetic, not a guarantee of plant availability, crop response, safety or suitability. Nutrient release, placement, soil, weather and timing matter. Do not mix incompatible products or infer compatibility from matching NPK numbers.
Frequently asked questions
What do the NPK numbers mean?
The three label percentages refer to nitrogen (N), available phosphate as P₂O₅ and soluble potash as K₂O. They are not the elemental phosphorus and potassium percentages. Check the actual product label.
Why not apply all the bags?
Whole-bag purchasing is rounded up. Apply only the calculated product mass; keep the remainder according to the label. Emptying every purchased bag may exceed the entered targets.
Can one product match all targets?
Only when the remaining nutrient targets and the fertilizer grade have matching proportions. Selecting one nutrient as the dose basis may under- or over-supply the others. A different grade or an adviser-designed multi-product plan may be needed.
Sources & References
USDANutrient management, soil stewardship and conservation planning resources.
FAOPlant nutrition, fertilizer use and integrated nutrient management references.University of Georgia ExtensionFertilizer calculations and nutrient management methods.Independent references, not endorsements. UGA: understanding fertilizer labels. No institutional review or universal safe application threshold is claimed.
Turn nutrient targets into a precise fertilizer plan.