Grass Seed Calculator
Enter your lawn area, pick a grass type and choose whether you are seeding a new lawn or overseeding an existing one — this calculator tells you how much grass seed to buy: the total weight, the number of bags, how much you will have left over, and the cost. Everything runs in your browser; nothing you type leaves your device.
Choosing a grass type auto-fills a typical seeding rate you can edit, so you do not have to remember whether tall fescue goes down at 7 pounds per 1,000 square feet or Kentucky bluegrass at 3. Add a zone for each part of the yard, switch between metric and imperial at any time, or flip to Coverage mode to work backwards from seed you already have.
Every rate here is a typical starting point — always check the rate printed on your seed bag, which can differ for coated, blended or pre-treated seed.
How to use the grass seed calculator
Grass seed is spread at a rate — a weight of seed per unit of area — so the seed you need is simply your lawn area multiplied by that rate. New lawns are seeded at the full rate; overseeding a thin but existing lawn uses about half of it.
Choosing a grass type only sets a sensible default rate; it never changes your measured area. The rate stays editable so you can match your seed bag exactly, and the bag size and prices are optional.
How to calculate grass seed in 5 steps
- Choose unitsPick metric (m², g/m², kg) or imperial (ft², lb per 1,000 ft², lb) at the top. You can switch later and every entry, including the seeding rate, converts in place.
- Pick a grass typeChoose your grass — tall fescue, Kentucky bluegrass, ryegrass, Bermuda and more — to auto-fill a typical seeding rate. The rate stays editable, so match it to your seed bag if the label differs.
- Set the goalChoose New lawn for bare soil or Overseed for a thinning existing lawn. Overseeding applies an editable multiplier (about 0.5×) to the new-lawn rate.
- Add your zonesAdd a zone per area, choose its shape (rectangle, L-shape, circle, triangle or a known area) and enter the dimensions. The areas sum across every zone.
- Read the resultsThe panel shows total seed weight and bag count as the headline numbers, plus the actual weight bought and the leftover. Add a bag or per-weight price for cost, or switch to Coverage mode to see how far seed you already have will go. Export CSV or print a plan.
Worked example: a two-zone lawn
A common job is a front and back lawn seeded together. Measure each zone, add them up, multiply the total area by your seeding rate, then divide by the bag weight and round up to whole bags. The calculator draws each zone to scale and totals them for you.
How much seed by grass type
Seeding rate is the single biggest driver of how much seed you buy, and it varies several-fold by grass type. Large-seeded and vigorous grasses like tall fescue, ryegrass and bahiagrass go down heavy; fine putting-green bentgrass and most warm-season grasses need far less seed per square foot.
New lawn vs overseeding
A brand-new lawn needs a full seeding rate to cover bare soil. Overseeding — dropping seed into an existing but thinning lawn — uses roughly half that rate, because the established grass is already doing part of the job. The goal toggle applies an editable multiplier (about 0.5× by default), so the same grass type gives you two rates from one setting.
Bags and leftover
Seed is sold in whole bags, so your order rounds up to the next bag and you end with a little left over. The calculator shows the exact weight you need, the actual weight you buy, and the leftover — handy for planning a second pass or keeping some back to patch thin spots later.
Round up to whole bags — and expect a little leftover.
| Seed needed | 28 lb |
| Actual bought (3 × 10 lb bags) | 30 lb |
| Leftover | 2 lb |
Always read your seed bag
The rates built in here are typical figures to get you started — your bag is the authority. Two caveats catch people out most often.
Buffalograss rates vary widely depending on whether the seed is sold as untreated burs or as cleaned, pure-live-seed — check which you have before trusting a single rate.
Coated, pelletized or pre-treated seed weighs more than raw seed for the same number of live seeds, so a bag of coated seed covers less than its weight suggests. Use the net weight and rate printed on your bag.
Frequently asked questions
How much grass seed do I need?
Measure your lawn area and multiply it by the seeding rate for your grass type. For a new lawn, tall fescue is about 7 lb per 1,000 ft², Kentucky bluegrass about 3, and ryegrass about 7 — so a 2,000 ft² tall-fescue lawn needs roughly 14 lb. Enter each zone and pick a grass type and the calculator totals the weight, bags and cost for you, adding any waste allowance you set.
How much grass seed per square foot?
Seeding rates are usually quoted per 1,000 square feet. Divide by 1,000 for a per-square-foot figure: a 7 lb per 1,000 ft² rate is 0.007 lb (about 3.2 g) per square foot. The calculator does this for you and lets you switch to g/m² for metric.
What is the overseeding rate?
Overseeding a thin but existing lawn uses about half the new-lawn rate for the same grass, because the established grass already covers part of the ground. Choose Overseed and the calculator applies an editable multiplier — about 0.5× by default — to the new-lawn rate.
What's the difference between a new lawn and overseeding rate?
A new lawn is seeded on bare soil at the full rate so the seed alone must cover the ground. Overseeding drops seed into a living lawn to thicken it, so it needs only about half as much. Same grass type, roughly double the seed for a new lawn versus an overseed.
How many bags of grass seed do I need?
Divide your total seed weight by the bag weight and round up to whole bags. If you need 28 lb and buy 10 lb bags, that is three bags (30 lb) with about 2 lb left over. The calculator counts bags for the bag size you choose and shows the leftover.
How much area does a bag of grass seed cover?
It depends on the grass type and rate. Coverage is the bag weight divided by the seeding rate: a 10 lb bag at 7 lb per 1,000 ft² covers about 1,400 ft² for a new lawn, or roughly double that when overseeding at half the rate. Switch to Coverage mode to enter a weight or a number of bags and read the area directly.
What is the seeding rate for different grasses?
Typical new-lawn rates per 1,000 ft² are about 3 lb for Kentucky bluegrass, 7 lb for tall fescue, 4 lb for fine fescue, 7 lb for perennial ryegrass, 1.5 lb for Bermuda, 2 lb for zoysia and 10 lb for bahiagrass. These are starting points — the calculator fills one in when you pick a grass, and you can edit it to match your seed bag.
Does coated or pre-treated seed change the amount?
Yes. Coated, pelletized or pre-treated seed weighs more than raw seed for the same number of live seeds, so a bag of coated seed covers less ground than its weight alone suggests. Always use the net weight and seeding rate printed on the bag rather than a generic figure.
Does it work in metric and imperial?
Both. Switch units at the top and every value converts in place — area in square feet or square metres, rate in pounds per 1,000 square feet or grams per square metre, and weight in pounds or kilograms.
Is the calculator private?
Yes. Every calculation runs entirely in your browser. Nothing you enter is sent to any server, and your project is saved only in your own browser's local storage.