Product needed (lbs) = Desired nutrient (lbs) / (NPK% / 100)
Fertilizer labels show N-P-K (nitrogen-phosphorus-potassium) as percentages by weight. A 50-lb bag of 10-10-10 contains 5 lbs each of N, P₂O₅, and K₂O. To apply 1 lb N per 1000 sq ft with 10-10-10: need 10 lbs of product per 1000 sq ft. Lawns typically need 2-4 lbs N/1000 sq ft/year, split into 3-4 applications. Always follow soil test recommendations — excess phosphorus causes water pollution. Apply evenly with a calibrated spreader. Water in lightly after application. Slow-release fertilizers reduce burn risk and provide sustained feeding. Organic options (compost, bone meal, blood meal) improve soil health long-term.