This grass seed calculator works out how many pounds of grass seed to buy from your lawn’s area and grass type — using the standard seeding rates in pounds per 1,000 sq ft, with separate rates for a new lawn and for overseeding an existing one.

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Rates Are Per Area Because Seeds Aren’t Per Pound

The seeding-rate table looks arbitrary until you know what drives it: seeds per pound varies sixfold across lawn grasses (bluegrass ~1.4 million/lb, perennial ryegrass ~240,000/lb, tall fescue ~230,000/lb), so any honest rate must be stated as pounds per unit AREA for each species — the target is plants per square foot, not weight per square foot. The standard extension rates are: tall fescue 6–8 lb/1,000 sq ft new (this page uses 8), Kentucky bluegrass 4–5, perennial ryegrass 7–9, fine fescues 5–6, hulled Bermuda 8–10, with overseeding at roughly half. The defaults run the most common job in American lawns: 5,000 sq ft of new tall fescue → 40 lb of seed — two standard 20 lb bags, a result worth having before the garden-center trip, since both under-buying (thin stand, weeds win the gaps) and over-buying (seedling crowding, disease pressure, wasted money) are failure modes with receipts.

Two adjustments the honest planner makes after this calculation: purity and germination (the seed tag’s PLS — pure live seed — percentage; a bag at 85% PLS needs dividing by 0.85, so 40 lb becomes 47 lb of bagged product), and shape reality (measure the lawn, not the lot: house, driveway, beds and patio come out of the area or the leftover seed goes stale in the garage — seed keeps a year or two cool and dry, losing germination steadily, which quietly taxes next year’s overseeding math too). Timing matters more than either: cool-season grasses want early fall (warm soil, cool air, weed pressure collapsing), warm-season grasses late spring — the finest rate arithmetic cannot rescue bluegrass sown into a July drought.

Worked Examples (Verified)

  • Defaults: 5,000 sq ft tall fescue, new lawn → 40.0 lb.
  • Same lawn, overseeding: 4 lb/1,000 → 20.0 lb.
  • Quarter-acre bluegrass: 10,890 sq ft × 5 lb/1,000 = 54.5 lb.
  • PLS correction: 40 lb at 85% pure live seed → buy 47 lb of bagged seed.

Grass Seed Discipline

  • Divide by PLS (germination % × purity % from the seed tag) when precision matters — bag weight is not seed weight.
  • Seed-to-soil contact is the rate multiplier nobody prints: dethatch, core-aerate or slit-seed before overseeding, or double-check why the first lawn thinned.
  • Never exceed new-lawn rates “for insurance”: crowding invites damping-off and pythium, and seedlings compete each other thin.
  • Calibrate the spreader on a driveway sweep: half the seed in each of two perpendicular passes hides spreader error and skips.
  • Keep seed dry and cool; a garage summer costs roughly 10–20% germination — last year’s bag is a discounted product whether the store says so or not.

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Frequently Asked Questions

How much grass seed do I need per 1,000 square feet?

By species, for a new lawn: tall fescue 6–8 lb, Kentucky bluegrass 4–5 lb, perennial ryegrass 7–9 lb, fine fescue 5–6 lb, hulled Bermuda 8–10 lb per 1,000 sq ft. Overseeding takes about half those rates. The spread exists because seed size does — bluegrass seed is tiny (~1.4 million per pound) so fewer pounds carry enough plants. Enter your area and grass type and this calculator returns the pounds for your job, e.g., 40 lb for 5,000 sq ft of new tall fescue.

How much seed for a 5,000 sq ft lawn?

At the standard new-lawn rates: 40 lb of tall fescue or perennial ryegrass, about 25 lb of Kentucky bluegrass, 30 lb of fine fescue, or 50 lb of hulled Bermuda. Overseeding the same area takes roughly half. Then adjust for the bag’s pure-live-seed percentage if you want the stand the rate table promises: divide by PLS (a 40 lb target at 85% PLS means buying 47 lb). Measure the actual lawn area — lot size counts the house and driveway, which grow no grass.

What’s the difference between seeding and overseeding rates?

Overseeding rates are about half of new-lawn rates because the existing turf is half the finished product: you’re filling gaps and thickening, not creating a stand from bare soil. There’s a second, physical reason — seed broadcast onto existing grass lands partly on foliage and thatch, where it can’t germinate, so effective delivery is lower per pound; dethatching, aerating or slit-seeding before overseeding recovers most of that loss and is worth more than bumping the rate ever is.

Can you put down too much grass seed?

Yes. Over-seeded lawns germinate into overcrowded seedlings that compete for light and water, stay spindly, and invite fungal diseases like damping-off that thrive in dense, damp stands — the lawn can end thinner than a correctly seeded one. The rate table is calibrated to produce the right plants-per-square-foot; “extra for luck” breaks the calibration. If you have leftover seed, store it cool and dry for next fall’s overseeding rather than doubling down today.

When is the best time to plant grass seed?

For cool-season grasses (fescue, bluegrass, ryegrass): early fall is the professional answer — soil still warm for fast germination, air cooling (less stress), weed seeds largely done for the year, and two cool seasons of root growth before summer. Spring is the acceptable second. For warm-season grasses (Bermuda, zoysia): late spring into early summer, when soil is reliably warm. The rate this calculator gives assumes sane timing; seed sown into drought or frost mostly feeds birds and the following year’s weed bank of excuses.

What is pure live seed (PLS)?

The fraction of a seed bag that is both the labeled species and alive: PLS = purity % × germination % from the seed tag. A bag at 95% purity and 90% germination is 85.5% PLS, meaning 14.5% of what you spread is inert filler, weed seed and dead seed. Professional specifications buy on PLS pounds; home calculations that ignore it systematically under-seed by 10–20%. This calculator gives target live-seed pounds — divide by the bag’s PLS to get bag pounds.

How do I calculate lawn area for seeding?

Break the lawn into rectangles and triangles, compute each in square feet (length × width; triangles half that), and subtract house footprint, driveway, walks, decks and planting beds from the lot total. Most suburban “quarter-acre lots” (10,890 sq ft) carry 5,000–7,500 sq ft of actual lawn. Irregular yards: measure the two longest perpendicular extents and multiply by ~0.8 as a shape allowance. A measuring wheel or your county parcel map’s aerial view beats pacing it off — a 20% area error is a 20% seed error.

Is this grass seed calculator free?

Yes — free, instant, no sign-up. Enter area, grass type and job type for the pounds of seed to buy.