Rates are pure-seed standards — coated seed (many retail bags) is ~50% coating by weight, so buy accordingly. Seed must touch soil and stay moist 2–3 weeks; those two rules are 90% of success.
Copy this code into your page. Free to use with the credit link.
advertisement
The seeding math
lbs of seed = rate for your grass × (sq ft ÷ 1,000) × job factor overseeding = ½ the new-lawn rate · patching = a little heavy
Seed rates differ 4× between grasses because growth habits differ: bluegrass spreads sideways by rhizomes and fills in; fescue and rye grow in bunches and only thicken where seed lands. That's the whole reason "how much seed" has no one answer — and why the bag's generic coverage claim can be badly wrong for your grass.
A worked example
Overseeding 5,000 sq ft of perennial rye: 8.5 lbs per 1,000 halved for overseeding = about 21 lbs — a 25-lb bag with a little left for patching. The same area as a NEW rye lawn wants ~43 lbs, and as a new bluegrass lawn just 13 — the grass choice moves the bill more than the lawn size does.
Give it a fighting chance
Seed-to-soil contact first (mow short, rake hard or aerate), starter fertilizer the same day — the fertilizer calculator handles the dose — then keep the surface moist with short daily waterings until germination, tapering to deep-and-rare. And mark the calendar: no pre-emergent within 8–12 weeks of seeding in either direction, unless the label says seeding-safe.
Frequently asked questions
How much grass seed do I need per square foot?
It depends on the grass more than the lawn: Kentucky bluegrass seeds at 2–3 lbs per 1,000 sq ft while tall fescue needs 8–10 — a 4× difference, because bluegrass spreads to fill gaps and fescue doesn't. Pick your grass above and the calculator applies the right rate.
Do I need less seed for overseeding than a new lawn?
Yes — about half. The existing grass fills most of the canopy, so overseeding just thickens it. Using new-lawn rates on an existing lawn wastes half the bag and crowds seedlings into competing with each other.
Why did my grass seed not grow?
The big four: seed never touched soil (it must contact dirt — mow low and rake or aerate first when overseeding), it dried out (new seed needs the top half-inch moist for 2–3 weeks, usually light watering 1–2× daily), it went down at the wrong temperature (cool-season grass germinates at 50–65°F soil; wait for early fall or spring), or a pre-emergent from earlier in the year is still blocking ALL seeds — that's its job.
When is the best time to plant grass seed?
Cool-season grasses (bluegrass, fescue, rye): early fall is king — warm soil, cool air, and the seedling gets fall + spring before its first summer. Spring is second-best. Warm-season (bermuda, zoysia): late spring once soil passes ~65°F. Summer seeding of cool-season grass mostly feeds the birds.