Fertilizer Calculator
Work out how much fertilizer to spread for a lawn or bed from the N-P-K on the bag, the area and the nitrogen rate you want, with bags needed and cost. Set the rate by nitrogen or by the phosphate or potash a soil test asks for, and see what one bag covers and the nutrients that go down with it.
Your numbers
The three numbers on the bag, e.g. 24-0-11: percent of nitrogen, phosphate (Pâ‚‚Oâ‚…) and potash (Kâ‚‚O) by weight.
Pounds of the nutrient per 1,000 ft². Blank for nitrogen uses 1 lb, the top of the 0.5 to 1 lb per application that LSU AgCenter and Iowa State give for lawns; your soil test or the bag's label may say less.
For the season's total: the same rate repeated. 1 for a single job.
Weight on the bag, in pounds.
Fertilizer to spread
–
- Rate
- –
- Bags
- –
- One bag covers
- –
- Nutrients per 1,000 ft²
- –
- As elemental P and K
- –
- Nutrients for the whole area
- –
- Area
- –
The calculation runs in your browser and ParrotNotes does not store your numbers. They sit in the page address so you can bookmark or share the result.
How fertilizer rates are worked out
Lawn fertilizer rates are given in pounds of a nutrient per 1,000 square feet, almost always nitrogen. To turn that into pounds of product, divide by the nutrient's percentage as a decimal: 1 lb of nitrogen from a 24-0-11 product is 1 ÷ 0.24 = 4.17 lb per 1,000 square feet. Multiply by the lawn's area in thousands of square feet for the total, and divide by the bag weight for the bags.
The other two numbers then tell you what goes down with it. At 4.17 lb of 24-0-11 per 1,000 square feet you also apply 4.17 × 0.11 = 0.46 lb of potash and no phosphate. If a soil test asks for a set amount of phosphate or potash instead, switch the rate to that nutrient and the same division applies, as LSU AgCenter describes.
Reading the N-P-K on the bag
The analysis printed on a fertilizer bag is three percentages by weight: nitrogen (N), phosphate (Pâ‚‚Oâ‚…) and potash (Kâ‚‚O). A 50 lb bag of 20-5-10 holds 10 lb of nitrogen, 2.5 lb of phosphate and 5 lb of potash; the rest is the other material in the granule.
Recommendations are written in the same oxide terms, so you rarely need the elemental figures. When you do, LSU AgCenter gives the conversion: phosphorus = P₂O₅ × 0.44 and potassium = K₂O × 0.83. The calculator shows both.
Pounds of product for 1 lb of nitrogen
Pounds of fertilizer per 1,000 square feet that put down 1 lb of nitrogen, by the first number on the bag, and the square feet a 50 lb bag covers at that rate. Rutgers prints the same kind of table in its fact sheet.
| Nitrogen on the bag | lb per 1,000 ft² | ft² per 50 lb bag |
|---|---|---|
| 10% | 10 | 5,000 |
| 16% | 6.25 | 8,000 |
| 20% | 5 | 10,000 |
| 24% | 4.17 | 12,000 |
| 26% | 3.85 | 13,000 |
| 29% | 3.45 | 14,500 |
| 32% | 3.13 | 16,000 |
| 46% | 2.17 | 23,000 |
How much nitrogen, and how often
LSU AgCenter and Iowa State Extension put a lawn application at 0.5 to 1 lb of nitrogen per 1,000 square feet, and the calculator starts at 1 lb when the field is left blank. For water-soluble nitrogen, Rutgers' fact sheet says a typical recommendation is only 1 lb for a single application; slow-release fertilizers, natural organics or controlled-release products, feed over a longer period and may be used at higher rates.
That is why a season's nitrogen is split into several applications rather than put down at once. Enter the number of applications to see the season's product and bags. Where the product label gives a different rate, the label comes first.
For lawn care and landscaping sales: what to write down
On the property walk, note the turf area of each section (front, back, side strips), what the soil test said, the product and analysis you plan to use, the number of visits in the program and anything the owner raised: bare patches, pets, kids, a well nearby. The numbers from the calculator then go straight into the quote.
Sources, each read on 2026-10-30. Results are estimates; the product's label and your soil test decide:
- Penn State Extension: Calculations Used to Determine the Amount of Fertilizer Needed to Treat Turf (worked examples, bag coverage)
- LSU AgCenter: Calculating Fertilizer Application Rates (N-P-K as N, Pâ‚‚Oâ‚…, Kâ‚‚O; 0.44 and 0.83; 0.5 to 1 lb N per application)
- Iowa State University Extension: How much fertilizer should I apply to my lawn? (0.5 to 1 lb N per 1,000 sq ft)
- Rutgers NJAES FS839: How to Calculate the Amount of Fertilizer Needed for Your Lawn (soluble N per application, slow release)
More for landscaping and home services sales: Landscaping sales, Home improvement sales.
The lawn program is agreed on the property walk
Square footage, what the soil test showed, which product and how many visits all come up while you walk the property with the owner. Record the walk in ParrotNotes and get a transcript, a summary and the action items, so the quote matches what you agreed.
Get Started FreeRelated tools
- Grass Seed CalculatorWork out how much grass seed a lawn needs by grass type, new lawn or overseeding, in pounds and bags, plus the fertilizer for the same area.Open the tool
- Mulch CalculatorWork out how many cubic yards or bags of mulch your beds need from their size and depth, with coverage per yard and the cost.Open the tool
- Square Footage CalculatorWork out square footage for rectangles, L-shaped rooms, triangles and circles, add rooms together, and convert to square yards, square meters and acres.Open the tool