Garden Lawn fertilizer calculator
Fertilizer is sold by product weight but applied by nutrient weight, and the two are very different. A 50 lb bag of 24-0-4 contains 12 lb of actual nitrogen. Getting this wrong is the most common cause of both burnt lawns and disappointing results.
How this is calculated
Pounds of product per 1,000 sq ft = target lb of nitrogen ÷ (%N ÷ 100). Multiply by your area in thousands of square feet.
Source: The 1 lb N per 1,000 sq ft standard rate follows university extension turf guidance
Worth knowing: One application should rarely exceed 1 lb of nitrogen per 1,000 sq ft, and quick-release nitrogen at that rate on a hot day will burn. Slow-release products are more forgiving. Do not fertilize before heavy rain — it runs straight off into waterways, and several US states restrict application dates for exactly that reason.
Common questions
What do the three numbers mean?
Nitrogen, phosphorus and potassium, as a percentage of the bag by weight. A 24-0-4 bag is 24% nitrogen, no phosphorus, 4% potassium. Nitrogen drives leaf growth and is the number this calculation uses.
Why is phosphorus often zero?
Many US states restrict or ban phosphorus in lawn fertilizer because runoff drives algal blooms in lakes and rivers. Established lawns rarely need it. A soil test will tell you if yours is genuinely deficient.
Can I just use the setting on the spreader?
Spreader settings printed on a bag are a starting point, not a guarantee — they vary by spreader model, walking speed and even humidity. Calibrate by weighing out the amount for a known area and checking how far it actually goes.
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