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Soil & Fertilizer
Use Calculator Fertilizer Dosage Calculator
Calculate fertilizer product required from a user-supplied nutrient target, product analysis and field area.
Soil & Fertilizer Calculators
NPK Fertilizer Calculator
Estimate the compound fertilizer rate needed to meet user-entered nitrogen, phosphorus and potassium targets.
Free agriculture calculator
No signup requiredNPK Fertilizer Calculator
Your results
How to use the NPK Fertilizer Calculator
- Enter the requested field, crop, animal, equipment, or cost information.
- Keep every value in the unit shown beside its field.
- Select Calculate and review each result and assumption.
- Verify important decisions with local records, labels, extension guidance, or a qualified adviser.
Formula and method
Required product rate is the largest of N target ÷ N fraction, P₂O₅ target ÷ P₂O₅ fraction, and K₂O target ÷ K₂O fraction.
The highest individual nutrient requirement controls the compound rate; the results show nutrients supplied and potential excess.
Worked example
A 15-15-15 product meeting a 60 kg N/ha target needs 400 kg/ha and also supplies 60 kg/ha each of P₂O₅ and K₂O.
Understanding the result
Treat the calculated values as a planning estimate. Compare them with your field records, product information, local conditions and operational capacity before acting.
Important: A single compound may oversupply one nutrient. Verify the nutrient plan and environmental limits locally.
Frequently asked questions
What happens if the fertilizer contains 0% of a required nutrient?
The calculator stops and warns that the selected product cannot supply that nutrient instead of silently ignoring the requirement.
Why can a compound fertilizer oversupply one nutrient?
A single compound has a fixed nutrient ratio. The rate needed to meet the most limiting nutrient can therefore supply more of another nutrient than the entered target.
What do positive nutrient differences mean?
A positive difference means the calculated compound rate supplies more of that nutrient than the entered target.
Should this calculator set my fertilizer recommendation?
No. Enter targets from an appropriate soil test, crop plan, label or qualified adviser and verify local nutrient-management requirements.