Fertilizer Calculator
How many bags of fertilizer for your lawn
Feeding your lawn? Enter the area to estimate how many bags of fertilizer you need, based on a typical bag's coverage.
Lawn fertilizer coverage is a nitrogen rate, not an area
The nitrogen rate lawn professionals work to is measured in pounds of fertilizer per 1000 square feet, derived from the NPK numbers on the bag.
Almost every lawn fertilizer calculator asks how many square feet a bag covers. That question has no fixed answer, and treating it as though it does is how people over- and under-feed lawns.
The standard unit in turf management is pounds of actual nitrogen per 1,000 ft², and 1 lb N per 1,000 ft² is a normal single application. How much product that takes depends entirely on the first number on the bag:
lb of product per 1,000 ft² = (target lb N × 100) ÷ nitrogen %
| Analysis | Nitrogen | lb per 1,000 ft² | A 40 lb bag covers |
|---|---|---|---|
| 10-10-10 | 10% | 10.00 lb | 4,000 ft² |
| 16-4-8 | 16% | 6.25 lb | 6,400 ft² |
| 24-0-4 | 24% | 4.17 lb | 9,600 ft² |
| 29-0-5 | 29% | 3.45 lb | 11,600 ft² |
| 32-0-4 | 32% | 3.13 lb | 12,800 ft² |
| 46-0-0 (urea) | 46% | 2.17 lb | 18,400 ft² |
The spread is the point. A 40 lb bag of urea covers more than four times the area a bag of 10-10-10 does at the same nitrogen rate. Any "one bag covers 5,000 ft²" figure is only true for one particular analysis at one particular rate — and for common 24% lawn feed it is out by nearly half.
What the NPK numbers mean
The three numbers are percentages by weight of nitrogen, phosphorus and potassium. Nitrogen drives leaf growth and colour, phosphorus supports roots and establishment, potassium builds stress and disease hardiness.
- Nitrogen is the one you dose against. Everything else follows from the N rate.
- Phosphorus is often zero on modern lawn products, and in many US states it is restricted by law on established lawns because of runoff into waterways. A middle number of 0 is deliberate, not a deficiency.
- Slow-release nitrogen is listed separately on the label as a percentage of the total. A product with more than half its N in slow-release form feeds for weeks instead of days and is far less likely to burn.
How much per year, and when
| Grass | Per year | Applications | Main season |
|---|---|---|---|
| Tall fescue | 2 to 4 lb | 3 to 4 | Autumn |
| Kentucky bluegrass | 3 to 5 lb | 3 to 4 | Autumn |
| Fine fescue (low input) | 1 to 2 lb | 1 to 2 | Autumn |
| Bermuda | 4 to 6 lb | 4 to 5 | Summer |
| Zoysia | 2 to 4 lb | 2 to 3 | Summer |
Never apply more than 1 lb of nitrogen per 1,000 ft² in a single application of quick-release product; that is the threshold above which burning becomes likely. Split the annual budget into several lighter feeds instead. For cool-season grasses the most valuable feed of the year is in autumn, not spring — spring nitrogen pushes top growth at the expense of roots just before summer stress arrives.
Spreading it evenly
- Halve the rate and make two perpendicular passes. This is the single best technique for avoiding stripes, and it costs nothing.
- Walk at a steady pace and shut the hopper before you stop or turn.
- Broadcast spreaders cover faster and blend overlaps better; drop spreaders are more precise near beds and paths but stripe badly if you misjudge a pass.
- Calibrate rather than trusting the dial. Spreader settings on a bag are approximate and vary between machines. Weigh out enough product for a known area and check it runs out about where it should.
- Sweep granules off paths and drives back onto the lawn. Anything left on hard surfaces washes straight into the storm drain.
- Water it in after applying, unless it is a weed-and-feed that needs to stick to damp leaves.
- Never feed a dormant or drought-stressed lawn. Fertiliser cannot be used by grass that is not growing, and it will burn.
Feeding a new lawn instead? Use a starter fertiliser high in phosphorus with the grass seed calculator, and hold off weed-and-feed until the new grass has been mown two or three times.
How this fertilizer calculator works out its numbers
Product needed is (target lb N × 100) ÷ nitrogen % per 1,000 ft², scaled to your lawn area. Bag counts divide the total by the bag weight and round up.
- This replaces a fixed 5,000 ft² per bag assumption, which was only correct for one analysis at one rate and understated a common 24% product's coverage by nearly half. Coverage is an output here, not an input.
- Default target is 1 lb of nitrogen per 1,000 ft², the standard single application and the usual maximum for quick-release product.
- Nitrogen percent is the first N-P-K number on the bag, taken as a percentage by weight.
- Not modelled: the slow-release fraction, phosphorus and potassium rates, soil test results, and any state restriction on phosphorus. A soil test is the only way to know whether P and K are actually needed.
- Annual nitrogen budgets by grass type follow US extension-service guidance and vary by region, soil and how much clipping is returned to the lawn.
Reviewed September 2026.
Figures reviewed . Every worked example on this page is checked against the calculator above.
Fertilizer Calculator: frequently asked questions
How much fertilizer do I need for my lawn?
Work from nitrogen, not coverage. At the standard 1 lb of nitrogen per 1,000 ft², a 24% product needs 4.17 lb per 1,000 ft², so a 2,500 ft² lawn takes about 10.4 lb of product.
How much area does a bag of fertilizer cover?
It depends entirely on the analysis and the rate. A 40 lb bag of 24-0-4 covers 9,600 ft² at 1 lb N per 1,000, while the same bag of 10-10-10 covers only 4,000 ft². Generic 5,000 ft² figures are true for one product at one rate.
How do I calculate pounds of fertilizer per 1,000 square feet?
Multiply your target nitrogen rate by 100 and divide by the nitrogen percentage on the bag. For 1 lb N from a 24-0-4 product: 1 × 100 ÷ 24 = 4.17 lb of product per 1,000 ft².
What do the numbers on fertilizer mean?
The percentage by weight of nitrogen, phosphorus and potassium. A 24-0-4 bag is 24% nitrogen, no phosphorus and 4% potassium. Phosphorus is often zero because many states restrict it on established lawns to limit runoff.
How often should I fertilize my lawn?
Three to four light applications across the growing season for cool-season grass, totalling 2 to 4 lb of nitrogen per 1,000 ft² a year. Bermuda wants 4 to 6 lb across four or five feeds. Never exceed 1 lb N in a single quick-release application.
When is the best time to fertilize a lawn?
Autumn for cool-season grasses such as fescue and bluegrass, which is when the feeding does most good for root development. Summer for warm-season grasses like bermuda and zoysia. Spring nitrogen pushes leaf growth just before summer stress.
Will fertilizer burn my lawn?
It can, if you apply more than about 1 lb of quick-release nitrogen per 1,000 ft² at once, feed a dormant or drought-stressed lawn, or spill a concentrated patch. Slow-release products are far more forgiving, and watering in helps.
Should I use a drop or broadcast spreader?
Broadcast for speed and for blending overlaps on open lawn; drop for precision near beds, paths and water. Whichever you use, halve the rate and make two perpendicular passes to avoid striping.