Application rates are determined by multiplying the first number, which represents the percentage of nitrogen contained, times the weight of the bag. Using the ScienTurfic fertilizer, which has a formula of 20-20-10-2fe-3s, multiply the first number (20%) by the weight of the bag (20 lbs) which will equal 4 (lbs of nitrogen). If you want to apply 1 lb of nitrogen per 1000 square feet this bag will cover 4,000 square feet.