Grass Seed Calculator
Work out how much grass seed your lawn needs — by area, grass type, new lawn or overseeding, spreader method and slope — with bags to buy, total cost, and a downloadable PDF.
Based on standard university extension seeding rates in pounds per 1,000 sq ft. Overseeding uses roughly half the new-lawn rate. Always check the rate printed on your seed bag. For planning purposes only.
| Grass Type | Rate (lb/1k) | Total (lb) | Bags | Cost |
|---|
For a 5,000 sq ft lawn, new lawn rates, 50 lb bags. Real bag prices vary by grass type.
How to Use the Grass Seed Calculator
Work out how many pounds of seed your lawn needs — at the right rate for your grass, your job and your spreader — plus the bags to buy and what it costs, in four steps.
Enter your lawn size
Type the length and width and the area fills in automatically — or overwrite it with a figure you already know, minus the driveway, beds and anything else you won’t be seeding.
Pick the job and the grass
Choose a new lawn, overseeding or heavy patch repair, then your grass type. Rates differ enormously between species, so this is the input that moves the number most.
Set your spreader and conditions
Broadcast, drop, hand or slit seeder each waste a different amount. Flag a sloped lawn to add for washout, and set a waste percentage for overlap and edges.
Read the result and save it
See total pounds, bags to buy, leftover seed and cost per thousand square feet, compare every grass type side by side, and download the branded PDF.
What’s Included
Built on standard extension seeding rates, with every adjustment that changes how much seed actually leaves the spreader.
Ten grass types at extension rates
Bluegrass, fescues, ryegrass, mixes, Bermuda, zoysia, bahia, centipede and buffalo — each with its own pounds per thousand square feet, season and germination window.
New lawn, overseed or patch
Overseeding runs at roughly half the new-lawn rate and bare-patch repair goes heavier. Switch the job and every number updates rather than leaving you to halve it in your head.
Spreader, slope and waste factors
A slit seeder places seed precisely; hand broadcasting scatters it. Four method multipliers, a slope allowance for washout, and an overlap percentage you control.
Bags, leftovers and cost
Rounds up to whole bags the way you actually buy, shows how much seed you’ll have spare, and gives cost per pound and per thousand square feet for comparing products.
Full grass type comparison
A table showing pounds, bags and cost for every grass type on your exact lawn, with yours highlighted — the fastest way to see what switching species would cost.
Branded PDF report
Bundles your lawn details, the full rate calculation, bag and cost figures, the grass comparison table and seeding best practice into a clean two-page report.
By the Numbers
A quick snapshot of what this calculator covers under the hood.
cool and warm season
new, overseed, patch
each with its own factor
the standard unit
no sign-up needed
Built for “How Many Bags Do I Actually Buy?”
Seeding rates swing from half a pound to eight pounds per thousand square feet depending on the grass. Guessing costs you money or costs you the lawn.
New lawns from scratch
Seeding bare ground after construction or a full renovation? Get the full establishment rate for your species, the bag count, and a sense of what a different grass would cost instead.
Fall overseeders
Thickening a thin lawn each season? Overseeding runs at about half the new-lawn rate — buying at full rate wastes money and crowds the seedlings that do come up.
Patch repairers & price comparers
Fixing bare spots or weighing up seed brands? Price by the pound and per thousand square feet rather than by the bag, which is the only fair way to compare products.
Seed Once, Properly
Seven habits that decide whether seed becomes a lawn or becomes bird food.
- 1More seed is not a better lawn. Over-applying crowds the seedlings, which then compete for water and light and thin themselves out — often leaving a patchier result than the correct rate. Extra seed also washes away, feeds birds, and costs you money.
- 2Seed-to-soil contact beats everything. Seed sitting on thatch or hard ground rarely germinates however much you put down. Rake lightly, core aerate before overseeding, or use a slit seeder — contact matters more than quantity.
- 3Time it to the grass, not the calendar. Cool-season types go down in early fall, when soil is warm and weed pressure is falling; spring is second best. Warm-season grasses want late spring into early summer, once soil has warmed properly.
- 4Keep the top inch damp for two to three weeks. New seed has no roots, so light frequent watering beats deep soaking until it germinates. Letting it dry out once after the seed swells will kill it outright.
- 5Subtract what you’re not seeding. Driveway, patio, beds and the shed footprint all come out of the total. Measuring the lot instead of the lawn is the most common reason people buy too much.
- 6Read the bag before you trust any rate. Blends, coated seed and cheap fillers all change how much actual live seed you’re buying per pound, and the label rate reflects that. Where the bag disagrees with a general figure, follow the bag.
- 7Watch what else you put down. A starter fertilizer helps; most pre-emergent weed-and-feed products will stop your new grass germinating just as effectively as they stop weeds. Hold off on those until the new lawn has been mowed a few times.
Frequently Asked Questions
Answers to the most common questions about seeding rates, timing and germination.
How much grass seed do I need?
Seeding rates are quoted in pounds per 1,000 square feet, so divide your lawn area by 1,000 and multiply by the rate for your grass. A 5,000 square foot lawn of tall fescue at eight pounds per thousand needs about 40 pounds for a new lawn. The calculator does that, then adjusts for your spreader, slope and overlap allowance and rounds up to whole bags — because those adjustments are what separate the textbook figure from what you actually need to buy.
Why do seeding rates differ so much between grass types?
Mostly seed size. A pound of centipede or bermudagrass seed contains vastly more individual seeds than a pound of tall fescue, so it covers far more ground — which is why centipede goes down at a fraction of a pound per thousand square feet while fescue and ryegrass need eight. Spreading habit matters too: grasses that fill in by runners or rhizomes need fewer starting plants than bunch-type grasses, which only ever occupy the spot they germinated in. The comparison table shows the full spread across all ten types on your lawn.
How much seed do I need to overseed an existing lawn?
Roughly half the new-lawn rate. You’re filling gaps in existing turf rather than covering bare ground, and the established grass is already occupying most of the space, so the full rate simply wastes seed on ground that has nowhere for it to grow. Bare patch repair works the other way — those spots get more than the standard new-lawn rate because they’re genuinely starting from nothing and often sit in the poorest soil in the yard. Switching the purpose in the calculator applies the right multiplier for you.
When is the best time to plant grass seed?
It depends on whether your grass is cool-season or warm-season. Cool-season types — Kentucky bluegrass, the fescues, perennial ryegrass — do best sown in early fall, when soil is still warm, nights are cooling and summer weeds have stopped competing; spring is workable but leaves young grass facing its first summer with a shallow root system. Warm-season grasses like Bermuda, zoysia, bahia and centipede need warm soil to germinate at all, so late spring through early summer is the window, well ahead of dormancy. Each grass type in the calculator shows which season it belongs to.
Can you put down too much grass seed?
Yes, and it’s the most common seeding mistake. Seedlings sown too thickly compete with each other for water, light and nutrients, producing weak, spindly plants that thin out anyway — and dense stands hold moisture at the surface, which encourages seedling diseases. You end up spending more to get a worse lawn. The correct rate leaves each seedling room to tiller and fill in, which is what actually produces thick turf.
How long does grass seed take to germinate?
It varies by species and conditions. Perennial ryegrass is the sprinter, often up within a week, while tall fescue takes a week or two and Kentucky bluegrass, zoysia and buffalograss can take three to four weeks. Cold soil, dry conditions and poor seed-to-soil contact all stretch those windows. Because the slower grasses need moisture maintained for a month, patience matters more than anything you can add — and each type’s germination range is shown when you select it.