Thoughtful Calc

Grass Seed Calculator

How many pounds of grass seed you need, at published rates for your grass and project, mostly from university extension.

How do you want to measure?
For odd shapes, measure each part as a rectangle, add them up, and subtract the house, driveway, and beds.
Winter color means sowing ryegrass into a bermuda lawn in fall so it stays green while the bermuda is dormant.
The grass that’s growing now. Winter ryegrass is meant for bermuda only.
Use the grass named on the seed bag (for a mix, the one with the biggest share). Overseeding? Match what’s growing; a garden center can name it from a clump. Not sure what suits your area? Add your state below and the result lists grasses for it. St. Augustine comes only as sod or plugs: see the sod calculator.
The bag says which, often in the product name. Unhulled and coated seed need a higher rate.
Poor means soggy spots, hard-packed soil, or acidic soil (low pH on a soil test). It raises the overseeding rate by 50%, as university guidance suggests.
Crabgrass preventers and many “weed and feed” products stop grass seed from sprouting too.
Pick the bag you plan to buy to get a bag count. Small patch bags count as "Other".
From the seed label (optional): purity, germination, coating
The “Pure seed” % in the small table of percentages on the bag, usually on the back or side. If it lists several varieties of your grass, add them up.
The “Germination” % on the same table. If it lists several, use the one for the biggest pure-seed line.
Listed as “coating material” on coated seed labels. Use it only if you leave purity and germination blank; the purity figure already allows for coating. Not used for bermuda.
Adds a note on which grasses suit your area and when to seed. It doesn’t change the amount.
Add your prices (optional; we use typical prices otherwise)
Used instead of the pound price for the bag size you picked.

Why our numbers are more realistic

The seed calculators we looked at use one unsourced rate per grass and ignore the label on the bag. We checked our numbers against university extension publications instead. Here's what changes:

Typical calculatorThis calculatorWhy it matters
Some default tall fescue to 10 lb per 1,000 sq ft 7 lb, inside the 5-9 lb university range Most university guides put tall fescue between 5 and 9 lb. On 5,000 sq ft, 10 lb per 1,000 means 50 lb against 35 lb here. More isn't better: one university guide warns that too much seed gives "weak, poorly developed and disease-prone seedlings."
Overseeding is a flat half of the new-lawn rate University rates where they exist, and a clearly labeled estimate where they don't Where university guidance gives an overseeding rate, we use it. Where it doesn't, we use half the new-lawn rate and say so in your result, rather than passing it off as a published figure.
Same overseeding rate whatever the soil 50% more where germination conditions are poor Fewer seeds take hold in wet, packed, or acidic soil, so university guidance says to sow half again as much.
One bermuda number Hulled, unhulled, or coated Unhulled and coated seed need about twice the hulled rate, so one bermuda number is off for two of the three types.
Assumes every bag is the same quality Optional purity and germination from the label University guides suggest seed with 90%+ purity and 85%+ germination. Weaker seed has fewer live seeds per pound, so we raise the rate to make up the difference.
At least one lists St. Augustine as a seed type Points you to sod University guidance lists only sod and plugs for St. Augustinegrass.
Winter ryegrass treated like any overseeding, on any lawn A winter color option for bermuda lawns, with a warning for other grasses University guidance gives 5 lb per 1,000 sq ft into an established lawn, only on bermuda: ryegrass can damage centipede, zoysia and St. Augustine lawns in spring.

How this works

Pounds of seed = lawn area ÷ 1,000 × rate per 1,000 sq ft. The rate depends on the grass and the project:

  • New lawn or renovation: the new-lawn rate for your grass. Our defaults are picks inside the university ranges, not published numbers.
  • Thin lawn (overseeding): university guidance says about half the new-lawn rate for cool-season grass. We use 1 lb for Kentucky bluegrass and 3.5 lb for tall fescue. No source gives an overseeding rate for the other grasses, so they get half the new-lawn rate too, marked "our estimate."
  • Poor germination conditions (overseeding only): the overseed rate is multiplied by 1.5.
  • Winter color on bermuda: 5 lb of ryegrass per 1,000 sq ft, the rate university guidance gives for an established lawn, though it doesn't generally recommend overseeding home lawns at all.
  • Bags: pounds needed ÷ bag size, rounded up.
  • Seed label: enter purity and germination, and the rate is multiplied by (90% × 85%) ÷ (your purity × germination). It never drops below the university rate. This is our adjustment, not a published one: it assumes the university rates are meant for seed of about that quality. Coating percentage counts only when purity and germination are blank.
  • Your state (optional, not for winter color): adds a note on your turf zone (our grouping, from university sources), the grasses that suit it, and a seeding window, or a warning if your grass doesn't suit the zone. It never changes the amount.
GrassNew lawn (default)University rangeOverseed
Kentucky bluegrass21.5-31 (university: half)
Tall fescue75-93.5 (university: about half, 3-4)
Perennial ryegrass54-82.5 (our estimate)
Fine fescue43-62 (our estimate)
Bluegrass with 10-15% ryegrass3.53-41.75 (our estimate)
Shade mix4.54-52.25 (our estimate)
Bermuda, hulled10.5-1 (university); 1-2 (a former extension agent)0.5 (our estimate)
Bermuda, unhulled21-2 (university); 3-5 (a former extension agent)1 (our estimate)
Bermuda, coated22 (one university source)1 (our estimate, no source)
Zoysia (Z. japonica)1.50.5-30.75 (our estimate)
Centipede0.50.25-10.25 (our estimate)
Bahia85-10 (one source)4 (our estimate, no source)
Buffalograss, treated43-5 (another source says 1-3 for burs)2 (our estimate, no source)

All rates are pounds of seed per 1,000 sq ft. Turf-type tall fescue blends use the tall fescue row.

After you plant

University guidance agrees on the basics. Your result shows the watering rule for the grass you picked.

Cool-season grassWarm-season grass
Until it's upKeep the top inch of soil damp: light watering 1 to 4 times a day, about ⅛ to ¼ in of water a day in all.Light watering 2 to 3 times a day for the first 2 to 3 weeks.
Once it's growingAt about 2 in tall, water less often and more deeply.Water less often and more deeply as the roots grow.
First mowAt about 3 in tall, cutting to 2 to 2½ in.When it's a third taller than its usual mowing height, cutting back to that height. First mow at about 4 to 5⅓ in for bahia (usually mowed at 3 to 4 in), 2 to 2⅔ in for centipede (1½ to 2), 1⅓ to 4 in for zoysia (1 to 3), and ⅔ to 2 in for bermuda (½ to 1½).
FeedingStarter fertilizer: 0.5 lb of nitrogen per 1,000 sq ft, 3 to 5 weeks after the seedlings come up. Check your state's phosphorus rules; most that restrict it allow it for a new lawn.

Never cut off more than a third of the blade at once. Hold off on weed preventer until the new grass has been mowed a few times (see below).

Covering the seed: university guidance suggests about 80 to 100 lb of straw per 1,000 sq ft (two or three typical small bales), spread thin enough that some soil still shows. Use straw, not hay, which carries far more weed seed. On a slope, rain can wash seed downhill: use more straw, or an erosion-control blanket pegged down.

Weed preventer and new seed

Crabgrass preventers and many “weed and feed” products are pre-emergent weed killers: they stop seeds from sprouting, grass seed included. If one went down this year, find its active ingredient on the label before you seed. If you can't, wait 4 months.

Active ingredientSeeding after itPutting it on new grass
Prodiamine (Barricade is one brand)Wait 4 months or more; longer at high rates60 days after seeding or after the second mowing, whichever is later
PendimethalinWait 3 to 4 monthsOnce the lawn has filled in and been mowed at least 4 times
DithiopyrWait about 12 weeksAfter at least 2 mowings
Mesotrione (Tenacity)Labeled for use at seeding on most cool-season grasses; check your grass is listed; not for bentgrass; seedlings may turn white for 1 to 3 weeks4 weeks or 2 mowings after it comes up, whichever is later

Where the label gives a wait, follow it rather than this table. We found no preventer labeled for use at seeding on warm-season grass. University guidance says cool-season seed sown in late summer (mid-August to mid-September) does fine after a spring preventer.

Common questions

How much grass seed to overseed a lawn?

About half the new-lawn rate for cool-season grass. Pick "Thin lawn" and the calculator uses it. If over half the lawn is weeds, pick "Renovation" instead: you're really starting over.

Can I plant St. Augustine grass from seed?

No. University guidance lists only sod and plugs for it. Use the sod calculator.

Should I buy extra seed?

No. The rate is already the amount to spread, and more seed doesn't make a thicker lawn: crowded seedlings come up weak and catch disease. Keep a little back to patch bare spots that show up later.

What this doesn't cover

  • Seed mixes with an unknown blend. Choose the row for the grass that makes up most of the bag.
  • Soil preparation. Seeding dates appear only as a general window for your zone, and only if you choose a state.
  • Pasture, wildflower, and erosion-control mixes.
  • Plugs and sprigs.

Sources

Related calculators

Numbers last reviewed: October 9, 2026.