Lawn
Fertilizer Calculator
Turf guidance is written in pounds of nitrogen per 1,000 sq ft, but fertilizer is sold as a percentage analysis. This converts between them for any bag you have, enter the three numbers on the front.
Updated
Lawn area
Turf only. Fertilizer rates assume grass, including beds means over-applying nitrogen to plants that did not want it.
Area = length × width
Your fertilizer bag
The three numbers on the front are percentages by weight of nitrogen, phosphate, and potash.
1 lb is the standard single application. Use 0.5 for quick-release soluble sources.
Wants 2–4 lb N per 1,000 sq ft per year.
Enter your lawn size and bag analysis.
Build a feeding schedule
Give the assistant your grass type and region and it will lay out a season-by-season fertilizer program. Rates stay exactly as calculated.
Written by AI from the figures above. The quantities themselves are calculated deterministically and are never generated by AI. Check anything consequential, permits, utility locates, and chemical labels especially, before acting on it.
How this is calculated
What the three numbers mean
The N-P-K numbers are percentages by weight of nitrogen, phosphate (P₂O₅), and potash (K₂O). A 50 lb bag of 22-0-0 contains 22% nitrogen by weight, which is 11 lb of actual nitrogen. The rest is carrier and other ingredients.
That is why you cannot compare bags by price alone. A cheap 10-10-10 bag delivers less than half the nitrogen per pound of a 24-0-4, so the cost per pound of actual nutrient can run the other way from the shelf price.
lb of product = lb of nitrogen wanted ÷ (N% ÷ 100)
Setting the rate
One pound of actual nitrogen per 1,000 sq ft is the standard single application for most lawns. For quick-release soluble nitrogen, half a pound is safer, the burn risk is real and the growth surge is wasteful.
Annual totals vary by grass and by how much you want to mow. Fine fescue is content on 1–2 lb of nitrogen per 1,000 sq ft per year. Tall fescue and bluegrass want 2–4. Bermudagrass under high expectations can take 3–6. Centipedegrass genuinely wants very little, over-fertilising is the most common way it gets killed.
| Grass | Low input | High input |
|---|---|---|
| Centipedegrass | 0.5 | 2 |
| Fine fescue | 1 | 2 |
| Buffalograss | 0.5 | 2 |
| Bahiagrass | 1 | 3 |
| Tall fescue | 2 | 4 |
| Kentucky bluegrass | 2 | 4 |
| Zoysiagrass | 2 | 4 |
| St. Augustinegrass | 2 | 5 |
| Bermudagrass | 3 | 6 |
Phosphorus restrictions
Many US states restrict phosphorus on established lawns, because it runs off into waterways and drives algae blooms. The typical rule allows phosphorus only when establishing a new lawn or when a soil test documents a deficiency.
That is why so many lawn fertilizers now read 24-0-4 or 32-0-4, the middle number is deliberately zero. Check your state and municipality before buying anything with phosphorus in it for an established lawn.
Worked example
Applying 1 lb of nitrogen with a 24-0-4 bag
A 7,000 sq ft lawn, targeting 1 lb of actual nitrogen per 1,000 sq ft with a 24-0-4 product.
- Area in thousands
- 7,000 ÷ 1,000 = 7
- Actual nitrogen wanted
- 7 × 1 lb = 7 lb N
- Product needed
- 7 ÷ 0.24 = 29.2 lb
- Spreader rate
- 1 ÷ 0.24 = 4.2 lb of product per 1,000 sq ft
- Bags
- One 40 lb bag covers it
About 29 lb of product. Set the spreader to deliver 4.2 lb per 1,000 sq ft, and calibrate it on a measured strip rather than trusting the dial.
Frequently asked questions
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- What Fertilizer Numbers Really Mean (NPK and Lawn Fertilizer Math)Wondering what those fertilizer numbers mean? Here’s how to read NPK ratios, why phosphorus is often zero, and how to figure out the right amount for your grass.
- Slow Release vs Quick Release Fertilizer: What Actually Matters for Your LawnSlow release fertilizer feeds your lawn for weeks with less risk. Quick release acts fast but can burn and fades quickly. Here’s how to choose and apply the right one.
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- Perennial Ryegrass: Fast Green-Up, Smart Uses, and Where It Falls ShortPerennial ryegrass seed is your shortcut to a green lawn,if you use it right. Here’s how to seed, blend, and care for it, plus where it works and where it fizzles.