Online tools - Enviraj
This tool estimates fertilizer amounts (in Kgs) based on the percentage of nitrogen, phosphorus, and potassium in the selected fertilizer, area of lawn/farm in hectares, and the amount of nitrogen per hectare.

Fertilizer options to adjust phosphorus or potassium only

Phosphorus (P) Source
Triple Superphosphate (0-45-0)

Potassium (K) Sources
Potassium sulfate (0-0-50) i.e. Sulfate of potash or SOP
Potassium chloride (0-0-60) i.e. Muriate of potash

Don’t know your farm area? calculate it here with Google Map Developers Area Calculator.