Lawn Fertilizer Calculator — NPK Ratio & Nitrogen Rate
Fertilizer Needed
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N Applied
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P Applied
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K Applied
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NPK Ratio
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How to Calculate Lawn Fertilizer
Fertilizer (lbs) = (N rate x Area / 1000) / (N% / 100). NPK = Nitrogen, Phosphorus, Potassium percentages.
Most lawns need 2-4 lbs N per 1,000 sq ft/year across 3-4 applications. Max 1 lb N per 1,000 sq ft at once.
Cool-season grasses: feed fall and spring. Warm-season: late spring through summer. Water after applying.
Frequently Asked Questions
How much nitrogen should I apply?
0.5-1 lb per 1,000 sq ft per application, 2-4 lbs total per year.
What do NPK numbers mean?
Percentages of Nitrogen, Phosphorus, Potassium by weight. 24-4-12 means 24% N, 4% P, 12% K.
When should I fertilize?
Cool-season grasses: fall and spring. Warm-season: late spring through summer.
Can I over-fertilize?
Yes. It burns grass, promotes excessive growth, and can contaminate waterways.