About the Garden Fertilizer Calculator

Fertilizer labels list N-P-K percentages — the fraction of the bag that is nitrogen, phosphorus, and potassium by weight. The golden rule of fertilizing is to dose by the nitrogen requirement, not by bag weight. A lawn needs about 1 lb of actual nitrogen per 1,000 sq ft; a 20-10-10 product delivers 0.20 lb of N per pound of product, so 5,000 sq ft needs 25 lb of product.

Reading the numbers

Higher nitrogen products (like 30-0-0) deliver the same N with less material, while balanced 10-10-10 suits vegetable gardens. Always verify the first number on the bag and adjust: product needed = (target N per 1,000 ft² × area/1,000) ÷ (N% / 100). This calculator applies exactly that formula with recommended targets for lawns, vegetables, flowers, and trees.