Fertilizer label decoder (oxide → elemental)
A guaranteed-analysis label reports P and K as oxides (P₂O₅, K₂O). Every ppm calculation needs the elemental fraction. Enter the label numbers to decode them. Do this first, before any dosing math.
Guaranteed analysis (label %)
Elemental composition
What the ppm engine actually uses
| Nitrogen (N) | 4.00% |
| Phosphorus (P) | 7.86% |
| Potassium (K) | 31.54% |
| Calcium (Ca) | 0.00% |
| Magnesium (Mg) | 0.00% |
| Sulfur (S) | 0.00% |
ppm preview
Concentration if you dissolve this product [II-3.1]
Store %element for the actual product form you buy (the hydrated salt), not the anhydrous salt. Epsom salt is MgSO₄·7H₂O at 9.9% Mg: the anhydrous figure (20.2%) would halve your weigh-out. When the label and a table disagree, trust the label.
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How do you convert P2O5 and K2O on a fertilizer label to elemental P and K?
Multiply the label's P2O5 percentage by 0.436 to get elemental phosphorus, and multiply K2O by 0.830 to get elemental potassium, since fertilizer labels report phosphorus and potassium in oxide form, not as the raw element your nutrient math needs. Nitrogen on the label is already elemental, so no conversion applies there. Enter your guaranteed analysis above for exact elemental percentages.