About Fertilizer Calculator
A fertilizer grade such as 15-15-15 gives the percentage by weight of nitrogen (N), phosphate (P₂O₅), and potash (K₂O). To supply a target amount of nitrogen, divide the rate by the nitrogen fraction: product per hectare = target N ÷ (N % ÷ 100). The same product then delivers phosphate and potash in proportion to its grade. Rates should come from a soil test and local crop guidance, which this calculator does not replace.
How to use Fertilizer Calculator
- Fill in "Target nitrogen rate", "Field area", "Nitrogen in product" and "Phosphate in product", and the other options.
- The result appears below and updates as you type.
- Copy the result with the copy button, or download it as a file where that is offered.
Questions about Fertilizer Calculator
How do I convert P₂O₅ and K₂O to elemental P and K?
Multiply P₂O₅ by 0.436 to get elemental phosphorus, and K₂O by 0.830 to get elemental potassium. Fertilizer labels use the oxide forms by convention, while some soil test reports use the elemental forms.
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