Fertiliser & Nutrient Calculator
Work out how much fertiliser to apply, and the nitrogen, phosphorus and potassium it delivers.
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total fertiliser needed
| Nitrogen (N) applied | – |
|---|---|
| Phosphorus (P) applied | – |
| Potassium (K) applied | – |
Fertiliser and nutrient calculator
This calculator tells you how much fertiliser to apply over an area, and how much actual nitrogen (N), phosphorus (P), and potassium (K) that delivers based on the product’s NPK ratio. Enter your area, the recommended application rate, and the NPK percentages from the packaging to feed your lawn, beds, or crops correctly.
Understanding NPK
The three numbers on fertiliser packaging — for example 12-5-8 — are the percentages of nitrogen, phosphorus, and potassium by weight. Nitrogen drives leafy green growth, phosphorus supports roots and flowering, and potassium improves overall health and disease resistance. Knowing the actual amount of each nutrient applied helps you avoid over- or under-feeding.
Applying fertiliser correctly
Always follow the application rate on the product, as too much fertiliser can scorch plants and pollute waterways. Spread it evenly and water it in unless told otherwise. To measure your area accurately, use our area calculator, and to prepare beds, the garden soil calculator.
Frequently asked questions
What does a 12-5-8 fertiliser mean?
It contains 12% nitrogen, 5% phosphorus, and 8% potassium by weight. The rest is filler and other nutrients.
Disclaimer: General guidance only. Follow the manufacturer’s instructions for your specific product and plants.