Reading the numbers on the bag
Every fertilizer bag shows three numbers, like 24-0-6. They are the percentage by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O). A 15 lb bag of 24-0-6 contains 3.6 lb of nitrogen, no phosphate and 0.9 lb of potash.
Planning the rest of the job? Use the Lawn area calculator and the Grass seed calculator too.
How does the calculation work?
Product (lb) = area ÷ 1,000 × nitrogen rate ÷ (N% ÷ 100)
A 5,000 ft² lawn fed 1 lb of nitrogen per 1,000 ft² with 24-0-6: 5 × 1 ÷ 0.24 = 20.8 lb of product, so two 15 lb bags.
In metric, rates are given in grams of nitrogen per m². 1 lb per 1,000 ft² is about 4.9 g/m².
How much nitrogen?
Most lawns need 2 to 4 lb of nitrogen per 1,000 ft² across the whole year, split into several feeds. Always follow the product label and any local rules on fertilizer use.