Lawn
Lawn Fertilizer Calculator
Convert your lawn size and fertilizer N-P-K into pounds of product per application, with timing.
Per application
Water in after applying, and wait at least 4-6 weeks before the next feeding unless the label says otherwise.
How the calculation works
Fertilizer rates are set by nitrogen content, not total product weight, because nitrogen is the nutrient that most affects growth and the one most likely to cause harm if overapplied. The formula is straightforward: divide your lawn area by 1,000, multiply by your target pounds of nitrogen per 1,000 sq ft, then divide by the fertilizer's nitrogen percentage to get pounds of product.
For example, a 5,000 sq ft lawn targeting 1 lb N per 1,000 sq ft needs 5 lb of actual nitrogen. With a 32-0-4 fertilizer (32% nitrogen), that means 5 ÷ 0.32 ≈ 15.6 lb of product spread evenly over the lawn.
Annual nitrogen budgets by grass type
| Grass type | Annual lb N / 1,000 sq ft | Best timing |
|---|---|---|
| Kentucky bluegrass | 3-4 lb | Split across spring and fall; avoid heavy summer feeding |
| Tall fescue | 2-4 lb | Fall-weighted, with a light spring feed |
| Perennial ryegrass | 3-4 lb | Similar to fescue — fall and spring, light summer |
| Bermudagrass | 3-5 lb | Late spring through summer during active growth |
| Zoysiagrass | 2-4 lb | Late spring through midsummer only |
| St. Augustinegrass | 2-4 lb | Spring through summer, avoid late fall feeding |
A sample cool-season feeding schedule
- Early spring (as grass greens up): 0.5-0.75 lb N per 1,000 sq ft — light feed, avoid pushing top growth before roots wake up.
- Late spring: optional light feed if the lawn looks pale, 0.5 lb N per 1,000 sq ft.
- Early fall: the most important feed of the year, 1 lb N per 1,000 sq ft, to rebuild roots after summer stress.
- Late fall: a final 'winterizer' feed, 0.5-1 lb N per 1,000 sq ft, boosts root reserves for spring green-up.
Avoiding fertilizer burn and runoff
Keep quick-release nitrogen applications at or below 1 lb per 1,000 sq ft, water it in promptly, and never apply before heavy rain, which washes nutrients into storm drains and waterways. Slow-release and organic fertilizers release nitrogen more gradually and tolerate slightly higher single-application rates, but always defer to the specific product label.
What does the first number on a fertilizer bag mean?
The three numbers are the N-P-K ratio by weight: nitrogen, phosphorus (as P2O5), and potassium (as K2O). A 32-0-4 bag is 32% nitrogen, 0% phosphorus, and 4% potassium by weight — the rest is filler that helps spread the product evenly.
Why does lawn fertilizer target 'lb of nitrogen per 1,000 sq ft' instead of a total weight?
Nitrogen is the nutrient that drives grass growth and greening, and it is also the one most likely to burn the lawn or run off into waterways if overapplied. University turf programs express recommendations as nitrogen per 1,000 sq ft so the rate stays consistent regardless of which product or N percentage you buy.
How much nitrogen should my lawn get per year?
Cool-season lawns (fescue, bluegrass, ryegrass) typically need 2-4 lb of nitrogen per 1,000 sq ft per year, split across 2-4 applications. Warm-season lawns (bermuda, zoysia, St. Augustine) typically need 2-5 lb per year, applied mainly during their active summer growing season.
Can I apply too much fertilizer in one go?
Yes — more than about 1 lb of nitrogen per 1,000 sq ft in a single quick-release application risks burning the grass. Slow-release or organic products are more forgiving and can sometimes go on a bit heavier; always check the bag's own rate table.
Last reviewed February 2026