Grass Seed Calculator
A pound of bermudagrass seed covers about five times the ground a pound of tall fescue does, so a single rule of thumb for every grass gets it wrong. Pick your grass and whether you're starting from bare soil or overseeding, add your lawn areas, and this calculator works out the pounds of seed, the bags to buy and the cost. The default rates come from university extension guides, and you can always swap in the rate printed on your bag.
New-lawn rate: 6–8 lb per 1,000 sq ft (Penn State 6–8 lb; NC State 6 lb).
Leave blank to use 7 lb. If your seed bag lists a rate, type it here. The label always wins.
Net lawn area: —
Optional buffer for spreader overlap and touch-ups. Extension rates already cover a normal seeding, so keep this small.
Both numbers are on the seed tag. They show how much of each bag can actually grow.
Your seed amount will appear here
Choose new lawn or overseeding, pick your grass, add your lawn areas, then click calculate.
Seeding rates by grass type
New-lawn rates in pounds of seed per 1,000 sq ft, as published by university extension services. The calculator's default is the middle column. For overseeding it cuts the rate by 25% for a thin lawn or 50% for a lawn that is mostly filled in.
| Grass | Published range | Default | Source |
|---|---|---|---|
| Cool-season | |||
| Tall fescue (turf-type) | 6–8 | 7 | Penn State; NC State uses 6 |
| Kentucky bluegrass | 1.5–3 | 2 | NC State 1.5–2; Penn State 2–3 |
| Perennial ryegrass | 4–5 | 4.5 | Penn State |
| Fine fescue | 4–5 | 4.5 | Penn State; Purdue 3–6 by type |
| Tall fescue + bluegrass mix | 5 + 1 | 6 | NC State |
| Bluegrass + perennial ryegrass mix | 2–3 | 2.5 | Penn State; NC State 2.5 |
| Sun & shade mix (fine fescue, bluegrass, ryegrass) | 4 | 4 | Penn State |
| Warm-season | |||
| Bermudagrass (seeded types) | 1–2 | 1.5 | NC State |
| Zoysiagrass (seeded cultivars) | 1–2 | 1.5 | NC State |
| Centipedegrass | 0.25–0.5 | 0.4 | NC State; Alabama Extension |
| Bahiagrass | 5 | 5 | NC State |
| Buffalograss (burrs) | 1.5–2 | 1.75 | Kansas State |
| St. Augustinegrass | not sold as seed | NC State | |
Coated seed weighs more per seed, so a coated product often lists a higher rate than these. When your bag gives a rate, use it.
Quick Answer
Seed needed (lb) = lawn area in sq ft ÷ 1,000 × seeding rate. For a new lawn, extension guides use about 6 to 8 lb per 1,000 sq ft for tall fescue, 1.5 to 3 lb for Kentucky bluegrass, 4 to 5 lb for perennial ryegrass and 1 to 2 lb for bermudagrass. For overseeding, NC State suggests 25 to 50% less.
How It Works: Formula & Variables
Seed (lb) = (Lawn area ÷ 1,000) × Seeding rate × (1 + extra % ÷ 100)
- Lawn area
- sum of added areas minus subtracted areas, in sq ft
- Overseeding rate
- new-lawn rate × 0.75 (thin lawn) or × 0.5 (mostly filled in)
- Bags
- round up (seed lb ÷ bag weight in lb)
- Coverage per bag
- bag weight ÷ seeding rate × 1,000 sq ft
- Pure live seed
- purity % × germination % ÷ 100
- Metric
- 1 lb per 1,000 sq ft ≈ 4.9 g/m²; 1 lb = 0.454 kg
Worked Examples
Example 1: new tall fescue lawn
A 5,000 sq ft bare-soil lawn seeded with tall fescue at 7 lb per 1,000 sq ft: 5 × 7 = 35 lb of seed. In 20 lb bags that is 2 bags, with about 5 lb left for patching thin spots later.
Example 2: overseeding a bluegrass lawn
An 8,000 sq ft Kentucky bluegrass lawn that is mostly filled in. The new-lawn default of 2 lb drops by half to 1 lb per 1,000 sq ft, so 8 × 1 = 8 lb of seed, or two 5 lb bags.
Example 3: centipedegrass, mixed with sand
A 3,000 sq ft centipede lawn at 0.4 lb per 1,000 sq ft needs 3 × 0.4 = 1.2 lb of seed. Seed this small is hard to spread evenly on its own, so Alabama Extension suggests mixing each pound with 20 lb of dry sand. That means about 24 lb of sand for this lawn.
Key Concepts
Seed size drives the rate: Rates are set to get a target number of seedlings, about 1,000 to 2,000 per 1,000 sq ft according to Penn State. Tall fescue seed is large, so it takes several pounds. Centipede seed is tiny, so a fraction of a pound does the job.
Bunch grasses don't fill gaps: Tall fescue and perennial ryegrass grow in clumps and can't spread sideways, so bare areas in those lawns have to be reseeded. Spreading grasses such as bermuda and zoysia can close small gaps on their own.
Not every grass comes as seed: St. Augustinegrass and most fine-textured hybrid bermudas are planted as sod, sprigs or plugs. Only a handful of zoysia cultivars can be seeded.
Common Mistakes
Using the new-lawn rate to overseed: Seeding into existing turf at the full rate wastes seed and crowds the seedlings, and Penn State links overly dense stands to more disease. Drop the rate by 25 to 50%.
Applying one rate to every grass: A blanket 10 lb per 1,000 sq ft is already above the extension range for tall fescue (6 to 8 lb). For bluegrass it is several times too much, and for bermuda or centipede it is far more than that.
Seeding in the wrong season: NC State says seeding outside the recommended dates raises the chance of failure, and it doesn't recommend late winter or spring seeding for cool-season grass. Warm-season seed needs a full growing season to establish before cold weather arrives.
Judging seed by bag price alone: Check purity and germination on the tag. Low pure live seed means you pay for filler and dead seed.
Frequently Asked Questions
It depends heavily on the grass. Extension guides put turf-type tall fescue at 6 to 8 lb per 1,000 sq ft for a new lawn, perennial ryegrass at 4 to 5 lb, fine fescue at 4 to 5 lb and Kentucky bluegrass at 1.5 to 3 lb. Warm-season seed is much lighter: 1 to 2 lb for bermudagrass and seeded zoysia, and only 0.25 to 0.5 lb for centipedegrass. Bigger seeds need more pounds to give the same number of plants.
Less than for bare soil. NC State Extension suggests a rate 25 to 50% lower than the new-lawn rate when you seed into existing grass. Use the smaller cut if the lawn has a lot of bare patches and the bigger one if it is mostly filled in and you only want it thicker. NC State also notes that bare spots bigger than about 4 inches across won't fill in by themselves, so make sure those get seed.
No. Penn State Extension says normal rates are meant to give about 1,000 to 2,000 seedlings per 1,000 sq ft, and that very dense stands from heavy seeding get more disease. NC State gives the same warning for tall fescue and Kentucky bluegrass: higher rates can leave weak, thin turf.
No. NC State Extension says St. Augustinegrass seed is unavailable, so it has to be planted as sod, plugs or sprigs. Many retail calculators still list a seeding rate for it. If you want St. Augustine, use the sod calculator instead.
Divide the bag weight by the seeding rate and multiply by 1,000. A 20 lb bag of tall fescue at 7 lb per 1,000 sq ft covers about 2,860 sq ft. The same 20 lb of bermudagrass at 1.5 lb covers about 13,300 sq ft. The calculator shows coverage per bag for whatever grass and rate you choose.
Pure live seed (PLS) is the share of the bag that is the seed you paid for and will actually sprout. Multiply the purity % by the germination % from the seed tag and divide by 100. Penn State's example: 85% purity and 60% germination gives 51% PLS, so you would need about 2 lb of that seed to get 1 lb of live seed. A cheap bag can turn out to cost more per pound of live seed than a better one.
Cool-season grasses such as tall fescue, bluegrass, ryegrass and fine fescue do best seeded in early fall, with early spring as a weaker second choice. Warm-season grasses such as bermudagrass, zoysia, centipede and bahia go in from about April to July once the soil warms up. Buffalograss can go in during spring once the soil reaches 55°F.
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Sources
- Penn State Extension: Lawn Establishment (cool-season seeding rates and mixes, seedling density, pure live seed)
- NC State Extension: Carolina Lawns (cool- and warm-season seeding rates, 25 to 50% lower overseeding rate, planting dates, St. Augustinegrass)
- Purdue Extension TURF-64-W: Fine Fescues (seeding rates by fine fescue type)
- Alabama Cooperative Extension: Home Lawns, Centipedegrass (seeding rate, mixing with sand, planting window)
- Kansas State University: Planting Buffalograss and Controlling Weeds (burr seeding rate, timing, depth)