Lawn Fertilizer Calculator — Free Online Tool
Fertilizer bags list three numbers (N-P-K) — but how many bags does your lawn need? This lawn fertilizer calculator converts your lawn's square footage and target nitrogen rate into pounds of product.
What is the Lawn Fertilizer Calculator?
Lawn advice is given in pounds of nitrogen per 1,000 sq ft — typically 0.5 to 1 lb per application — because nitrogen (the first NPK number) drives green growth. A '24-0-0' bag is 24% nitrogen by weight, so delivering 1 lb of nitrogen per 1,000 sq ft takes about 4.2 lbs of that product.
More is not better: over-fertilizing burns grass, wastes money, and pollutes waterways. Measure your lawn (length × width, minus the house footprint and beds), calibrate your spreader, and never exceed label rates. Two lighter applications beat one heavy one.
How to use this calculator
- Enter your lawn area in square feet.
- Set the target nitrogen rate (lbs per 1,000 sq ft).
- Enter your fertilizer's nitrogen % (the first NPK number).
- Click Calculate Fertilizer.
Formula
Frequently asked questions
What do the three fertilizer numbers mean?
N-P-K: nitrogen (leaf growth), phosphorus (roots), potassium (overall health). A 24-0-0 bag is 24% nitrogen by weight.
How much nitrogen does a lawn need?
About 0.5–1 lb of actual nitrogen per 1,000 sq ft per application, 2–4 times a year depending on grass type and climate.
Can too much fertilizer kill grass?
Yes — excess nitrogen burns leaf blades ('fertilizer burn'), and excess phosphorus/potassium harms soil and waterways. Always follow label rates.
How do I measure my lawn's square footage?
Break it into rectangles: length × width for each section, add them up, then subtract the house footprint, driveway, and garden beds.