NPK fertilizer calculator

Enter your recommendation and the fertilizer grade. See how many kg/ha to apply, which nutrients are covered or short, and the cost.

Free, no sign-up

Before you use it

Works well for

  • Turning an N-P-K recommendation into kg/ha of a blend
  • Comparing blends by cost per hectare
  • Seeing which nutrient is short or in surplus

Not the right tool for

  • Making the recommendation — that comes from a soil test and an agronomist
  • Micronutrients and secondary nutrients (S, Ca, Mg)

How it works

A fertilizer grade like 04-14-08 means 4% N, 14% P₂O₅ and 8% K₂O by weight. To supply X kg/ha of a nutrient you need X ÷ (percentage ÷ 100) kg/ha of fertilizer.

By default the calculator picks the dose that covers all three nutrients — the one that needs the most fertilizer — and shows the surplus of the others. Tick the option to match one nutrient instead, and it shows what's still missing.

Example

Recommendation 30-80-60 with 04-14-08: N needs 750 kg, P₂O₅ 571 kg and K₂O 750 kg of fertilizer. Applying 750 kg/ha covers everything, with 25 kg/ha extra P₂O₅.

Filling gaps

When a nutrient is short, top it up with a straight fertilizer: urea (45% N), ammonium sulfate (20–21% N), triple superphosphate (41–46% P₂O₅) or potassium chloride (58–60% K₂O).

Frequently asked questions

Is it better to cover all nutrients or match one?

Covering all is simplest but may waste the nutrient in surplus. Matching the main nutrient and topping up the rest with straight fertilizers is often cheaper — compare both.

Does it account for nitrogen losses?

No. Losses depend on source, timing and weather — your agronomist's recommendation should already account for them.

Can I use elemental P and K?

Use oxide values (P₂O₅ and K₂O), the way fertilizer labels and most recommendations are written.