Fertilizer Calculator

Fertilizer calculators determine how much product to apply based on the nitrogen (N), phosphorus (P), and potassium (K) content stated on the bag (the NPK ratio). Over-application wastes money and risks plant burn and waterway pollution through nitrogen run-off

The calculator uses the standard published formula for fertilizer calc. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.

This calculator works with inches, square metres, percentages. You can enter values in the units shown — the calculator handles all conversions internally.

The core formula is: Amount (g) = (Area m² × N required g/m²) ÷ (N% / 100). Each step in the calculation is shown so you can verify the result manually.