The amount of grass seed you need depends on your lawn's size and the seed's germination rate

The standard recommendation is 3 to 6 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. The exact amount within that range depends on three things: whether you're starting from bare soil or filling in thin spots, the type of grass seed you're using, and the germination rate printed on the seed bag.

Most homeowners buy too little seed, then wonder why their lawn has bare patches. A lawn that germinates at 70 percent needs more seed than one at 90 percent to end up with the same density of grass. The seed bag label tells you the germination rate—look for "pure live seed" or "PLS" to know what percentage of the seed will actually grow.

Key Takeaways

  • New lawns need 3 to 6 pounds per 1,000 square feet; overseeding thin lawns needs 1 to 2 pounds per 1,000 square feet.
  • The germination rate on the seed bag determines how much seed actually grows, so lower germination rates require you to buy more seed.
  • Measure your lawn in square feet by multiplying length times width, then divide by 1,000 to find how many "thousand square foot" units you have.
  • Spreading seed too thin is the most common mistake—bare spots and thin coverage result from underseeding, not overseeding.
  • Cool-season grasses (fescue, bluegrass, ryegrass) and warm-season grasses (bermuda, zoysia, St. Augustine) have different seeding rates and seasons.

How to calculate the square footage of your lawn

Measure your lawn with a tape measure or use an online mapping tool. For a rectangular lawn, multiply the length by the width. For an irregular shape, break it into rectangles, calculate each one, and add them together.

Once you have the total square feet, divide by 1,000. A 5,000-square-foot lawn is 5 units of 1,000 square feet. If the bag says to use 4 pounds per 1,000 square feet, you multiply 4 × 5 = 20 pounds of seed for your whole lawn.

New lawns versus overseeding existing lawns

A new lawn starts on bare soil or heavily damaged ground. You need the higher end of the range—4 to 6 pounds per 1,000 square feet—because you're establishing grass from scratch and some seed will not germinate or will be lost to birds, wind, or poor soil contact.

Overseeding means spreading seed over an existing lawn to fill in thin spots, bare patches, or areas damaged by heat, drought, or foot traffic. You need less seed because existing grass is already there to compete with weeds. Use 1 to 2 pounds per 1,000 square feet, and focus on the thin areas rather than spreading evenly across the whole lawn.

Understanding germination rate and pure live seed

The seed bag label shows a germination percentage—usually between 70 and 95 percent. This tells you what fraction of the seeds in the bag will actually sprout under ideal conditions. A bag with 85 percent germination means 15 percent of the seeds are dead or dormant and won't grow.

If you buy seed with 70 percent germination, you need to buy more total seed to end up with the same number of growing plants as seed with 90 percent germination. Some bags list "pure live seed" or "PLS percentage," which combines germination rate with the percentage of the seed that is actually the grass species you want (not filler or weed seed). Use the PLS number if it's available—it's the most honest measure of what will actually grow.

Cool-season versus warm-season grass seeding rates

Cool-season grasses (tall fescue, perennial ryegrass, Kentucky bluegrass) are seeded in fall or early spring. These typically need 3 to 6 pounds per 1,000 square feet for a new lawn. Overseeding rates are 1 to 2 pounds per 1,000 square feet. Cool-season grasses germinate best when soil temperature is between 60 and 70 degrees Fahrenheit.

Warm-season grasses (Bermuda, zoysia, St. Augustine, buffalo grass) are seeded in late spring or early summer. Seeding rates vary more widely by species—Bermuda and zoysia may need 2 to 4 pounds per 1,000 square feet, while St. Augustine is often sold as sod rather than seed. Check the specific grass variety on your seed bag, because warm-season rates are not one-size-fits-all. These grasses need soil temperature above 70 degrees to germinate.

Common mistakes that lead to thin or patchy lawns

The most frequent error is buying too little seed. Homeowners often assume a 5-pound bag will cover their whole lawn, then spread it too thin and end up with bare spots. If the math says you need 20 pounds, buy 20 pounds—or buy 22 pounds to account for seed lost to birds or wind.

The second mistake is seeding at the wrong time of year. Cool-season grass seeded in summer will struggle in heat and drought before it's established. Warm-season grass seeded in spring before soil warms up will sit dormant or rot. Check your grass type and seed in the season when that grass germinates best.

A third mistake is poor seed-to-soil contact. Seed needs to touch soil to germinate. If you spread seed over thick thatch or dead grass without raking first, much of it will sit on top and dry out. For overseeding, rough up the soil with a dethatcher or rake, spread the seed, then lightly rake again so seed settles into the soil.

How to spread seed evenly across your lawn

A broadcast spreader (also called a rotary spreader) throws seed in a wide arc and covers ground quickly. It works well for large lawns but can create uneven coverage if you overlap passes or miss spots. A drop spreader releases seed directly below as you walk, giving you more control and even coverage, especially near edges and garden beds. Drop spreaders are slower but more precise.

For best results, divide your total seed amount in half. Make one pass going north to south, then a second pass going east to west. This crosshatch pattern fills in gaps and reduces the chance of missing strips. Walk at a steady pace and keep the spreader setting consistent throughout.

Frequently Asked Questions

Can I use the same seeding rate for all types of grass?

No. Cool-season and warm-season grasses have different seeding rates, and individual species vary. Always check the seed bag label for the recommended rate for that specific grass type. Bermuda, for example, needs less seed than tall fescue.

What happens if I spread too much seed?

Overseeding can lead to overcrowding, where seedlings compete for water and nutrients and many die off. It also wastes money and seed. Stick to the recommended rate for your situation—new lawn or overseeding—and you'll get a denser, healthier result than spreading seed too thick.

Should I buy seed with the highest germination rate available?

Higher germination rates mean fewer seeds wasted, so you can buy less total seed and still get good coverage. Seed with 90 percent germination is more efficient than 70 percent. However, price matters too—sometimes a lower-cost seed with 75 percent germination is a better value than premium seed at 95 percent, depending on the price per pound.

Do I need to adjust the seeding rate if my soil is poor?

Yes. Poor soil with low organic matter, compaction, or pH problems will reduce germination. Consider buying 10 to 20 percent more seed than the standard rate recommends, or improve the soil before seeding by adding compost and testing pH. Seed germinates best in soil that's been prepared.

Can I overseed in the middle of summer?

Not effectively. Cool-season grass seeded in summer heat will struggle to germinate and establish before fall stress arrives. Warm-season grass seeded too early will rot in cool spring soil. Seed in the right season for your grass type—fall or spring for cool-season, late spring or early summer for warm-season.