Water Soluble Fertilizer Calculator
Enter the fertilizer mass, the final solution volume, and the percentages printed on the label to see the theoretical nutrient concentrations. This is mass-balance arithmetic on the values you supply, not a feeding recommendation.
Last updated: September 26, 2026
Frequently asked questions
How is this different from the Fertilizer Calculator?
The Fertilizer Calculator works out how much product covers an area at an application rate. This tool starts from a mass dissolved in a final volume and reports the theoretical nutrient concentration in the solution.
Is P₂O₅ the same as phosphorus?
No. Labels state phosphate as P₂O₅, which contains about 43.64% elemental phosphorus. The calculator shows both the label form and the elemental equivalent.
Is K₂O the same as potassium?
No. Potash is stated as K₂O, which contains about 83.01% elemental potassium. The calculator shows both forms.
Why is mg/L treated as ppm?
For dilute aqueous solutions with a density close to 1 kg/L, 1 mg/L is approximately 1 ppm by mass. This breaks down for concentrated solutions.
What concentration should I use?
That depends on the plants, growth stage, water quality, and product, so this calculator does not suggest targets. Follow the product label and agronomic guidance for your crop.
Does it account for impurities or solubility limits?
No. It assumes the fertilizer dissolves completely and that the label percentages are accurate. Solubility limits and other ingredients are not modeled.