Fertiliser Calculator
Work out how much fertiliser a field or garden needs to supply the right nitrogen, phosphate or potash.
About the Fertiliser Calculator
Enter the area, the recommended dose of a nutrient in kg per hectare, which nutrient and its percentage in your fertiliser. The calculator gives the fertiliser to apply and the number of 50 kg bags.
Fertiliser labels give the grade as % N – % P₂O₅ – % K₂O. To supply a nutrient, divide the amount needed by the fertiliser's percentage of that nutrient. For example, 120 kg/ha of nitrogen from urea (46% N) needs 261 kg/ha of urea. Base the recommendation on a soil test (in India, the Soil Health Card).
The formula
Product (kg) = nutrient needed (kg) ÷ nutrient % × 100
Worked example
1 acre needing 120 kg/ha of nitrogen, from urea (46% N)
- Per hectare: 120 ÷ 0.46 = 260.9 kg
- 1 acre is 0.405 ha: 105.6 kg of urea
- About 3 bags of 50 kg
Questions people ask
What does 18-46-0 mean?
18% nitrogen, 46% phosphate (P₂O₅), 0% potash: DAP.
Is P₂O₅ the same as phosphorus?
No: P = P₂O₅ × 0.4364; K = K₂O × 0.8301.