Landscaping
Grass Seed Calculator
Enter your lawn size and this gives you the pounds of seed. New lawns take about three times what overseeding takes.
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| Lawn area | — |
|---|---|
| In thousands of sq ft | — |
| Seeding rate | — |
| Seed needed | — |
| Bags, rounded up | — |
What to buy
Paid links. If you buy through one, we earn a commission. Your price is the same. Nothing is listed here unless the calculator above says you need it.
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Grass seed
The pounds above assume the rate for the species you picked. Every bag prints its own new-lawn and overseeding coverage, so check it against this number.
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Starter fertilizer
New seed needs phosphorus to root. It is a different product from regular lawn feed, and applying the wrong one wastes the seed you just bought.
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Broadcast spreader
Hand-scattering gives you thin patches and wasted seed. The spreader setting is what turns pounds per thousand square feet into an even lawn.
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Straw or seed blanket
Only for new lawns on bare soil. Seed that dries out or washes away does not germinate, no matter how much you bought.
How to estimate grass seed
Seed is sold by weight and applied by rate, so the calculation is area divided by a thousand, times pounds per thousand square feet. The trap is that the rate is not one number. It changes with the species and it changes by a factor of three depending on whether you are starting a lawn or thickening one.
pounds = lawn area ÷ 1,000 × rate (lb per 1,000 sq ft)
overseeding rate = new-lawn rate ÷ 3Rates derived from Scotts' stated bag coverages. Their tall fescue mix works out to 9.09 lb per 1,000 sq ft for a new lawn.
Where the rates come from
Seed bags rarely print a rate. They print a coverage, which is the same information turned inside out, and you can recover the rate by division.
Scotts' Turf Builder Rapid Grass Tall Fescue Mix comes in a 16 pound bag stated to cover 1,760 square feet as a new lawn. Sixteen pounds over 1.76 thousand square feet is 9.09 pounds per thousand. Their Quality All-Purpose Mix is a 20 pound bag covering 2,665 square feet new, which is 7.5. Their bermudagrass is a 1 pound bag covering 330 square feet, which is 3.03.
Those three numbers are the rates in the seed selector, and they are worth internalising because they are so far apart. Bermuda takes a third of what fescue takes for the same ground.
Why species changes the number so much
It is seed size, not quality. Seeding rates are really about how many seeds land per square inch of soil. A pound of bermudagrass holds vastly more individual seeds than a pound of tall fescue because bermuda seed is tiny. The pounds on the bag are just the packaging.
This is also why you cannot carry a rate you remember from one lawn to a different bag. Check the coverage on the bag in your hand and divide, or use the selector above and confirm it against the label.
New lawn versus overseeding
This is the biggest lever on the page and the one most people get wrong in the expensive direction.
Look at the same three products. Tall fescue: 1,760 square feet new, 5,280 overseeding. All-purpose: 2,665 new, 8,000 overseeding. Bermudagrass: 330 new, 1,000 overseeding. Every one of those pairs is a three-to-one ratio to within rounding.
That consistency is useful. If a bag only prints one of the two numbers, you can derive the other with confidence. Overseeding takes a third, because you are filling gaps in existing turf rather than covering bare soil.
More is not better
It is tempting to over-apply on the theory that more seed makes a thicker lawn. It does the opposite.
Seedlings that germinate too close together compete with each other for water, light and root space. The result is spindly grass that is weaker and more prone to disease than a correctly seeded lawn. The rate on the bag is a recommendation, not a floor. Overseeding at the new-lawn rate wastes about two thirds of the bag and produces a worse result than doing it properly.
Measure the lawn, not the lot
Worth saying on its own, because it is the mistake that costs the most money and nobody catches it. A quarter-acre lot is about 10,900 square feet, but the lawn on it might be 4,000 once you take out the house, the driveway, the patio, the beds and the shed.
Walk it and measure the grass. Break odd shapes into rectangles and add them. Seeding at the right rate for an area you never measured is still the wrong amount of seed.
A quick cost check
A 60 by 40 lawn is 2,400 square feet. As a new tall fescue lawn at 9.09 pounds per thousand, that is 21.8 pounds, so two 20 pound bags. Overseeding the same lawn takes 7.3 pounds, comfortably one bag.
At $60 a bag that is $120 against $60. Same lawn, same seed, and the only difference is which job you are actually doing.
Common estimating mistakes
- Using the new-lawn rate to overseed. Triple the seed, worse lawn.
- Carrying a rate across species. Fescue and bermuda differ by a factor of three.
- Measuring the lot instead of the lawn. Subtract the house, the drive, the beds and the patio. People routinely over-buy by a third this way.
- Hand-scattering. Even coverage is the whole point of a rate. A spreader is what makes the number mean anything.
- Buying seed and skipping starter fertilizer. New seed needs phosphorus to root, and regular lawn feed is the wrong product.
Timing beats quantity
This is the one place where getting the measurement perfect will not save you. Seed sown at the wrong time of year fails regardless of the rate.
Cool-season grasses, which includes fescue and bluegrass, do best sown in late summer into early fall, when the soil is still warm but the heat has broken. Spring is the second-best window. Warm-season grasses like bermuda want late spring into early summer.
And water is not optional. New seed needs consistently moist soil until it germinates, which usually means light watering more than once a day for a couple of weeks. If you cannot commit to that, wait for a better window rather than buying seed you will watch die.
Questions
How much grass seed do I need per 1,000 square feet?
It depends on the species and on whether you are starting a lawn or thickening one. Working backwards from Scotts' own stated bag coverages: their tall fescue mix works out to about 9 pounds per 1,000 square feet for a new lawn, their all-purpose mix about 7.5, and bermudagrass about 3. Bermuda seed is much smaller, so a pound of it goes a long way.
How much less seed does overseeding take?
About a third of the new-lawn rate. This is consistent across Scotts' product line: their tall fescue bag covers 1,760 square feet as a new lawn and 5,280 when overseeding, their all-purpose bag 2,665 against 8,000, and their bermudagrass 330 against 1,000. All three are almost exactly a three-to-one ratio, which is a useful thing to know when a bag only prints one of the two numbers.
Can I just use more seed to get a thicker lawn?
No, and it works against you. Seedlings that come up too close together compete for water, light and root space, and the result is thin, weak grass that is more prone to disease. The rate on the bag is a recommendation, not a minimum. Overseeding at the new-lawn rate wastes money and produces a worse lawn.
Why do different grasses need such different amounts?
Seed size. A pound of bermudagrass contains vastly more seeds than a pound of tall fescue, because the individual seeds are far smaller. Seeding rates are really about how many seeds land per square inch, and the pounds are just how that gets sold. It is why you cannot carry one rate across species.
When should I seed?
For cool-season grasses like fescue and bluegrass, late summer into early fall is the strongest window, with spring second. For warm-season grasses like bermuda, late spring into early summer. Seeding at the wrong end of the year is the most common way a correctly measured bag of seed still fails.
Every constant on this page is logged with its source and the date it was checked in data/sources.md.