Calculator · nutrition
Fertilizer nutrient calculator
Convert between fertilizer mass and nutrient amount from a percentage grade, and between oxide (P₂O₅/K₂O) and elemental (P/K) notation.
Result
Enter values to see a result.
Formula & assumptions
Nutrient mass from fertilizer mass and grade
formula v1.0.0 · calc v1 · reviewed 2026-07-12nutrient = fertilizer_mass × (grade% ÷ 100)
Applies to: Any solid or liquid fertilizer expressed as a percentage grade.
Assumptions
- Grade is the guaranteed analysis percentage of the nutrient (N, P₂O₅, or K₂O) by mass.
Limitations
- Compound (N-P₂O₅-K₂O) grades express phosphorus as P₂O₅ and potassium as K₂O, not elemental P/K.
Sources: International Fertilizer Association (IFA) (opens in a new tab), Penn State Extension, The Pennsylvania State University (opens in a new tab)
Fertilizer mass for a target nutrient amount
formula v1.0.0 · calc v1 · reviewed 2026-07-12fertilizer_mass = target_nutrient ÷ (grade% ÷ 100)
Applies to: Any fertilizer expressed as a percentage grade.
Assumptions
- Grade is the guaranteed analysis percentage by mass.
Limitations
- Does not account for nutrient losses, placement, or availability.
Sources: International Fertilizer Association (IFA) (opens in a new tab), Penn State Extension, The Pennsylvania State University (opens in a new tab)
P₂O₅ to elemental P
formula v1.0.0 · calc v1 · reviewed 2026-07-12P = P₂O₅ × 0.4364
Applies to: Converting oxide-notation phosphorus to elemental phosphorus.
Assumptions
- Uses standard atomic masses (P 30.974, O 15.999).
Limitations
- Oxide vs elemental notation differ by country and product label.
Sources: International Fertilizer Association (IFA) (opens in a new tab)
K₂O to elemental K
formula v1.0.0 · calc v1 · reviewed 2026-07-12K = K₂O × 0.8301
Applies to: Converting oxide-notation potassium to elemental potassium.
Assumptions
- Uses standard atomic masses (K 39.098, O 15.999).
Limitations
- Oxide vs elemental notation differ by country and product label.
Sources: International Fertilizer Association (IFA) (opens in a new tab)
About this tool
- Compound grades express P as P₂O₅ and K as K₂O. This is an educational conversion, not a fertilizer recommendation.
Educational reference — not a prescription
- These calculators are for education and reference. The quality of any result depends entirely on the accuracy of the values you enter.
- Local agronomic conditions, legal requirements, product labels, and professional advice may override a general calculation.
- Results are not pesticide, fertilizer, irrigation, or veterinary prescriptions, and are not a substitute for advice from a qualified agronomist or your local extension service.