NPK Fertilizer Calculator

Work out how much nitrogen, phosphorus and potassium a fertilizer applies from its N-P-K grade and the amount spread, over a lawn or garden area. The grade (e.g. 10-10-10) lists percent N, P₂O₅ and K₂O by weight; the tool converts the oxide forms to elemental P and K, and reports the pounds applied per 1000 ft² (the standard application-rate unit). Also solves in reverse: enter a target nitrogen rate and get how much product to apply. Useful for lawn, garden and small-field planning. Pure arithmetic, in your browser.