Grass Seed Calculator
Pounds and bags of grass seed for a new lawn or an overseed, from the seeding rate on the label.
Grass seed is one of the few materials where buying too much is genuinely wasteful: germination rates fall fast after a season, so a half bag in the garage is money thrown away. Too little is worse, though. A thin seed bed lets weeds take the gaps, and you end up reseeding within a month.
The rate on the bag is pounds per thousand square feet, and it assumes a properly prepared seed bed. Broadcast by hand tends to run uneven — half the lawn gets double, half gets nothing. Split the seed into two passes at right angles to each other, and you will get closer to the label rate than any single pass achieves.
How this calculator works
Every field is editable and the result updates as you type — nothing is submitted anywhere, all the maths runs in your browser. That matters for a number you are about to spend money on: you can see exactly which input moved the answer, and by how much.
What this calculation assumes
Assumes the label rate for a standard blend on a properly prepared seed bed. Shaded areas, slopes, low-organic soil and late-season sowing all need a higher rate, and bare patches from washout are not counted.
Treat the result as an order-of-magnitude check rather than a final quantity. Product packaging changes, regional labour rates vary by a factor of two, and no calculator has seen your actual site.
Frequently asked questions
How much seed do I need per 1,000 square feet?
Four pounds for a new lawn, two pounds to overseed an existing one, both at label rates for a standard blend. Bump a new lawn to five or six pounds if you are seeding in autumn in a cold climate, or if the area is sloped and rain may wash seed into the low corner.
Should I add more seed to be safe?
No. Over-seeding causes competition between seedlings, and the result is weaker grass than a correct rate, not a thicker lawn. Seed also needs contact with soil and consistent moisture — neither of which extra seed supplies. Spend the difference on a starter fertiliser instead.
When is the best time to seed?
Early autumn in most temperate climates: the soil is still warm, nights are cooler, and autumn rain does the watering. Spring works but the new grass then has to survive its first summer while still shallow-rooted, which is why spring seedings often thin out in July.
Related calculators
Same category, and a couple you will probably need next.