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Fertilizer Calculator

Fertiliser needed for an area at a target nitrogen rate, from the NPK analysis.

Enter values

Results update as you type.

Result

Fertiliser needed

1.5 kg

Water it in after applying — undissolved granules on dry grass scorch the leaves.

Application rate
15 g/m²
Nitrogen applied
0.3 kg
Phosphorus applied
0.15 kg
Potassium applied
0.15 kg
NPK analysis
20-10-10
Cost
$4.50

About the Fertilizer Calculator

Fertiliser needed for an area at a target nitrogen rate, from the NPK analysis.

Also known as: lawn feed calculator, npk calculator, fertiliser rate, nitrogen application rate.

How to use this calculator

  1. Enter area, nitrogen target, nitrogen in the product, phosphorus (p) and the other fields.
  2. The result updates instantly as you type — press Calculate (or Enter) at any time.
  3. Review the breakdown shown under the main result.
  4. Use Copy result or Share to save the answer or send a link with your inputs.

Formula

product = area × nitrogen target ÷ nitrogen percentage

Worked example

Using the values pre-filled in the calculator above:

  • Area = 100 m²
  • Nitrogen target = 3 g N/m²
  • Nitrogen in the product = 20 %
  • Phosphorus (P) = 10 %
  • Potassium (K) = 10 %
  • Price per kg = 3

the calculator returns:

  • Fertiliser needed: 1.5 kg
  • Application rate: 15 g/m²
  • Nitrogen applied: 0.3 kg
  • Phosphorus applied: 0.15 kg