Fertilizer Calculator
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The rate is an editable typical figure. Follow the product label and any state or local fertilizer rules, which can limit nitrogen and phosphorus.
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How the fertilizer calculation works
Read the N-P-K grade on the bag
The three numbers are percent by weight of nitrogen, phosphate and potash. A 24-0-11 bag is 24% nitrogen.
Product per 1,000 sq ft = N rate ÷ N%
To apply 1 lb of nitrogen per 1,000 sq ft with 24-0-11: 1 ÷ 0.24 = 4.17 lb of product. NC State Extension gives the same rule as "divide 100 by the first number": 100 ÷ 16 = 6.25 lb of a 16-4-8 product.
Multiply by the area in thousands
A 10,000 sq ft lawn takes 10 × 4.17 = 41.7 lb, so one 50 lb bag covers one application.
Price it: product + labor, then markup
Add spreading time at your cost per hour for each round, then your markup. A 30% markup on cost is a 23% margin.
Worked example. A 10,000 sq ft lawn gets 1 lb of nitrogen per 1,000 sq ft from a 24-0-11 fertilizer: 1 ÷ 0.24 = 4.17 lb per 1,000 sq ft, or 41.67 lb in total. One 50 lb bag at $45 covers it. With 1 hour of labor at $45 the cost is $90, and a 30% markup prices the application at $117.
Fertilizer FAQ
How do I calculate how much fertilizer to use?
Divide the nitrogen rate you want by the nitrogen percentage, then multiply by the area in thousands of square feet. For 1 lb N with a 24% product on 10,000 sq ft: 1 ÷ 0.24 × 10 = 41.7 lb.
What do the three numbers on fertilizer mean?
They are the percentages of nitrogen (N), phosphate (P₂O₅) and potash (K₂O) by weight. A 50 lb bag of 24-0-11 holds 12 lb of nitrogen and 5.5 lb of potash.
How much fertilizer does my lawn need?
Work from nitrogen. NC State Extension suggests 2–4 lb of nitrogen per 1,000 sq ft a year for established tall fescue and Kentucky bluegrass, 3–6 lb for bermudagrass and much less for centipedegrass, given 0.5–1 lb at a time. At 1 lb N, a 24-0-11 product means 4.17 lb per 1,000 sq ft. A soil test and your state extension service refine this.
How much fertilizer per acre?
An acre is 43,560 sq ft, so multiply the per-1,000 sq ft amount by 43.56. At 1 lb N per 1,000 sq ft (43.56 lb N per acre), a 24-0-11 product takes 43.56 × 4.17 = 181.5 lb per acre, or four 50 lb bags.
How often should I fertilize my lawn?
It depends on the grass and how green you want it. In NC State's piedmont tables, a basic tall fescue program is three feedings (0.5, 1 and 0.5 lb N) for 2 lb a year, put down mainly in fall and spring; a high-maintenance bermudagrass program is six monthly 1 lb feedings in the growing season. Set Applications to price a season.
How many square feet does a 50 lb bag of fertilizer cover?
Divide the bag's nitrogen by your rate. A 50 lb bag of 24-0-11 holds 12 lb of N, which covers 12,000 sq ft at 1 lb N per 1,000 sq ft.
How do I use a liquid fertilizer?
The same way if the label gives N as percent by weight: work out pounds of product, then convert to gallons with the weight per gallon on the label.
Sources: NC State Extension: Carolina Lawns, A Guide to Maintaining Quality Turf in the Landscape