You need about 3 to 5 pounds of grass seed per 1,000 square feet for a new lawn, and 1 to 2 pounds per 1,000 square feet for overseeding an existing lawn. This translates to roughly 0.003 to 0.005 pounds per square foot for new lawns, but the exact amount depends on the grass species, the seed blend, and whether you are starting from bare soil or thickening an established turf.
Formula
The general formula for calculating how much grass seed you need is:
Seed needed (lb) = (Lawn area (ft²) × Seeding rate (lb per 1,000 ft²)) / 1,000
Where:
- Lawn area is the length × width of the area you are seeding, measured in square feet.
- Seeding rate is the recommended amount of seed per 1,000 square feet, which varies by grass type (see table below).
- Seed needed is the total weight of seed required, in pounds.
If your lawn is not a perfect rectangle, break it into rectangles and triangles, calculate each area separately, and add them together. For a triangle, the area is 0.5 × base × height.
Worked Example
Using the default values from the calculator above: a lawn that is 40 feet long and 25 feet wide, with a seeding rate of 5 pounds per 1,000 square feet.
- Calculate the lawn area: 40 ft × 25 ft = 1,000 ft².
- Apply the seeding rate: 5 lb per 1,000 ft².
- Since the lawn is exactly 1,000 ft², the seed needed is 5 lb.
The calculator gives 5.00 lb, which matches. If the lawn were 2,000 ft² at the same rate, you would need 10 lb.
Seeding Rates by Grass Type
Not all grass seed is created equal. Fine fescue has tiny seeds, so fewer pounds cover the same area, while tall fescue has large, heavy seeds and needs more weight per square foot. The following are typical ranges for new lawns (bare soil). For overseeding, use about half of these amounts.
- Kentucky bluegrass: 2–3 lb per 1,000 ft²
- Perennial ryegrass: 4–5 lb per 1,000 ft²
- Tall fescue: 6–8 lb per 1,000 ft²
- Fine fescue (creeping red, chewings, hard): 3–4 lb per 1,000 ft²
- Bermudagrass (hulled): 1–2 lb per 1,000 ft²
- Zoysiagrass: 1–2 lb per 1,000 ft² (often sold as sprigs or plugs instead)
- Centipedegrass: 0.5–1 lb per 1,000 ft²
These are general guidelines. The seed bag label is the most reliable source, as it is specific to the blend you bought. Always check the label for the “seeding rate� or “coverage� – it will tell you how many square feet the bag covers.
New Lawn vs. Overseeding
The biggest factor in how much seed you need is whether you are starting from scratch or improving an existing lawn.
New lawn (bare soil): You need the full rate listed above. The goal is to get good soil-to-seed contact and enough seed density to form a thick stand. If you under-seed, weeds will fill the gaps. If you over-seed, the seedlings compete for water and light, and you waste money.
Overseeding (existing lawn): Use about half the new-lawn rate. The existing grass is already there; you are just filling in thin spots or introducing a new variety (for example, overseeding a warm-season lawn with annual ryegrass in winter). Overseeding at the full new-lawn rate can smother the existing grass and create a patchy, clumpy look.
For spot repairs (a bare patch from a dog or a dead shrub), you can hand-sow at the new-lawn rate just on that patch, then lightly rake the seed in.
How to Measure Your Lawn Area
Accurate area measurement is the first step to buying the right amount of seed. Guessing can leave you short by a bag or two, which means a trip back to the store and a patchy lawn.
- Rectangular or square lawns: Measure length and width in feet, multiply them together.
- L-shaped lawns: Divide into two rectangles, calculate each, and add them.
- Circular areas: Measure the radius (half the diameter), square it, and multiply by 3.14.
- Triangular areas: Multiply base × height, then divide by 2.
- Curved borders: Approximate with straight lines; the error is usually small.
If you have a lawn that includes a garden bed or patio, measure the whole area and subtract the non-lawn portions. For most home lawns, measuring to the nearest foot is precise enough – a few square feet of error will not change the seed amount meaningfully.
Common Mistakes and How to Avoid Them
Even with the right seed amount, several common errors can ruin a new lawn:
- Not preparing the soil. Seed needs contact with soil to germinate. Rake the area to loosen the top 1–2 inches, remove debris, and level low spots before spreading seed.
- Seeding at the wrong time. Cool-season grasses (fescue, bluegrass, ryegrass) do best when soil temperatures are 50–65°F (early fall or spring). Warm-season grasses (bermuda, zoysia) need soil at 70–85°F (late spring/early summer). Check your local extension service for your region’s best dates.
- Forgetting to water. New seed must stay consistently moist until germination. That often means light watering 2–3 times a day for the first 2–3 weeks. If the seed dries out after it has started to sprout, the seedlings die.
- Using a spreader incorrectly. Set the spreader to the setting on the seed bag, and walk at a steady pace. Overlap slightly to avoid stripes. For small areas, a hand-held spreader works fine.
- Not raking or rolling after seeding. A light raking (or rolling with an empty lawn roller) presses the seed into the soil, improving germination. Seed left on the surface is eaten by birds or blows away.
- Buying by the bag, not by the pound. Bags come in different weights (often 3, 5, 10, or 20 lb). Always check the coverage on the label, not just the bag size.
What Happens If You Use Too Much or Too Little?
Under-seeding is the more common mistake. Too little seed means bare patches, which weeds quickly colonize. You will likely need to reseed those spots later, costing more time and money.
Over-seeding is less harmful but still wasteful. Seedlings grow too close together, competing for water, nutrients, and light. The result is a lawn that looks good for a few weeks but then thins out as weaker seedlings die. You also waste money on seed you did not need.
There is a happy medium. The rates in this article are proven for most home lawns. If you are on a steep slope or have heavy clay soil, use the higher end of the range – those conditions make germination harder. If you have excellent topsoil and irrigation, the lower end is fine.
Frequently Asked Questions
How many square feet does a 5 lb bag of grass seed cover?
It depends on the species. A 5 lb bag of Kentucky bluegrass (at 2–3 lb per 1,000 ft²) covers roughly 1,600–2,500 ft². The same 5 lb bag of tall fescue (at 6–8 lb per 1,000 ft²) covers only about 600–800 ft². Always read the label on the bag – it states the exact coverage for that blend.
Can I just throw grass seed on top of existing grass?
You can, but germination will be poor. The seed needs to touch soil, not sit on top of thatch or old grass blades. For best results, mow the lawn short, rake or dethatch to expose soil, spread the seed, and then roll or rake lightly. Water consistently afterward.
Should I use more seed if I have bare patches?
For a completely bare patch, use the new-lawn rate for that area. If the patch is just thin (you can still see some grass), use the overseeding rate. Applying the new-lawn rate to a thin but living lawn can suffocate the existing grass.
How long does grass seed take to germinate?
Most cool-season grasses germinate in 7–21 days, depending on soil temperature and moisture. Ryegrass is fastest (5–10 days), while Kentucky bluegrass can take 14–30 days. Warm-season grasses like bermudagrass take 7–14 days with warm soil. Keep the soil moist the entire time – if it dries out, germination stops.
Do I need to cover the seed with soil?
Not deeply, but a light covering helps. A thin layer (about 1/4 inch) of topsoil, compost, or a straw mulch keeps the seed moist and protects it from birds. Seed buried deeper than 1/2 inch will not germinate. A light raking after spreading is usually enough.
Is it better to seed in spring or fall?
For cool-season grasses (fescue, bluegrass, ryegrass), early fall is best – the soil is warm, the air is cool, and weeds are less aggressive. Spring seeding works but often requires more watering through summer. For warm-season grasses (bermuda, zoysia), late spring to early summer is ideal, when soil temperatures are consistently above 70°F.