The rate is published per 1,000 square feet — that is the whole trick
No seed bag says "this covers your lawn." It says something like 6 lb per 1,000 sq ft, because the bag has no idea how big your lawn is. So the arithmetic is one multiplication, done in two steps: divide your area by 1,000, then multiply by the published rate.
Pounds of seed = (area in sq ft ÷ 1,000) × rate in lb per 1,000 sq ft
A 5,000 sq ft lawn at 6 lb per 1,000 sq ft needs (5,000 ÷ 1,000) × 6 = 30 lb. That is it. Everything below is about picking the right rate and turning pounds into bags you can actually buy.
Seeding rates Extension services actually publish
Kansas State Extension puts tall fescue at 6 to 8 lb per 1,000 sq ft on new ground and Kentucky bluegrass at 2 to 3 lb. North Carolina State's Burke County office rounds the same two grasses to 6 lb and 2 lb respectively. The two disagree by a rounding, not by a principle: tall fescue seed is far larger, so it takes roughly three times the weight per acre of ground.
| Grass | New lawn | Overseeding | Source |
|---|---|---|---|
| Turf-type tall fescue | 6–8 lb | about half (3–4 lb) | K-State |
| Kentucky bluegrass | 2–3 lb | about half (1–1.5 lb) | K-State |
| KBG + tall fescue mix | 1 lb KBG + 5 lb tall fescue | — | NC State |
The third row is the one most calculators skip. If you are sowing a mix, you do not average the two rates — you apply each grass at its own share, so the total is 6 lb per 1,000 sq ft, of which 5 lb is fescue and 1 lb is bluegrass.
New lawn, overseeding, or shaded ground
K-State is explicit that the new-lawn figure is the ceiling, not the target for every job: about half as much goes down when you are overseeding an existing lawn, or seeding into shade. The reason is competition. In a new seedbed every seed has bare soil to land on; overseeding drops seed into a lawn that already has roots in it, and shaded ground germinates more slowly and supports fewer plants.
So three rates come out of one table: full rate for bare soil in sun, half rate for overseeding, and half rate again for shade. A 5,000 sq ft overseed of tall fescue lands at 15 lb, not 30 lb — and a bag bought on the new-lawn figure will sit half-used in the garage.
Three worked examples
5,000 sq ft, new tall fescue at 6 lb per 1,000 sq ft. 5,000 ÷ 1,000 = 5, times 6 = 30 lb. In 7 lb bags that is 5 bags (35 lb), which leaves 5 lb spare — enough to touch up a worn path or two. In 20 lb bags it is 2 bags (40 lb), and the 10 lb surplus is more than you need.
10,000 sq ft, overseeding tall fescue at half rate (3 lb per 1,000 sq ft). 10,000 ÷ 1,000 = 10, times 3 = 30 lb. The same 30 lb that covered 5,000 sq ft at full rate now stretches over twice the ground. Two 20 lb bags do it with 10 lb to spare.
2,500 sq ft, NC State mix of 1 lb bluegrass + 5 lb tall fescue. Bluegrass: 2,500 ÷ 1,000 = 2.5, times 1 = 2.5 lb. Fescue: 2.5 times 5 = 12.5 lb. Total 15 lb, bought as two separate bags because the two grasses are sold separately.
How far one bag actually goes
Working backwards is often more useful at the shelf than working forwards. Divide the bag weight by the rate and multiply by 1,000:
| Bag | at 2 lb/1,000 | at 3 lb/1,000 | at 6 lb/1,000 | at 8 lb/1,000 |
|---|---|---|---|---|
| 3 lb | 1,500 sq ft | 1,000 sq ft | 500 sq ft | 375 sq ft |
| 7 lb | 3,500 sq ft | 2,333 sq ft | 1,166 sq ft | 875 sq ft |
| 20 lb | 10,000 sq ft | 6,666 sq ft | 3,333 sq ft | 2,500 sq ft |
| 50 lb | 25,000 sq ft | 16,666 sq ft | 8,333 sq ft | 6,250 sq ft |
Read the 7 lb row against the 6 lb column and the practical warning appears: one small bag does not cover a normal suburban front lawn at a full tall fescue rate. It covers about 1,166 sq ft, which is a 34 by 34 ft patch.
What going too heavy or too light actually does
Both errors cost money, but they fail differently. K-State notes that over-seeding produces a lawn more prone to disease and to damage from stress: crowded seedlings compete for the same water and light, stay weak, and a thick mat of young plants holds moisture against the crown. Under-seeding fails the other way — the lawn comes up clumpy and thin, and because tall fescue is a bunch grass that does not spread sideways, bare gaps stay bare until you seed them again.
That asymmetry matters when you are choosing between a 6 and an 8 lb rate. Egging toward the higher end is the safer error on bare soil, where seed-to-soil contact is good. On a slope or a windy day, where some seed will be lost regardless, the higher end stops being optional.
Measuring the area before you buy anything
Every calculation above is downstream of one number you have to measure yourself. Break the lawn into rectangles and add them: length times width for each, summed. For a triangular corner, multiply the two short sides and halve it. For a circular bed, measure across and multiply the diameter by itself, then by 0.785.
Subtract what is not lawn — the driveway, the patio, the shed footprint, and any bed you are not seeding. A 10 % subtraction on a 5,000 sq ft lot is 500 sq ft, which at a full tall fescue rate is 3 lb of seed you would otherwise buy and waste. Measure once with a tape and write the numbers down; guessing from a property listing is how people end up two bags short on a Sunday.
After the seed is down
Clemson Cooperative Extension is blunt that establishment succeeds or fails on moisture in the first two weeks: keep the surface consistently moist without letting it puddle, watering lightly and often rather than deeply and rarely. Clemson also gives the straw figure people ask for — one bale, 60 to 80 lb, covers about 1,000 sq ft. That is one bale per 6 lb of tall fescue seed, which is a tidy way to remember the pair.
Two more things from the same factsheet worth planning for: seed needs contact with soil, not with thatch, which is why raking or core-aerating before sowing changes the result more than raising the rate does; and a starter fertiliser goes down at 1 to 2 lb of actual nitrogen per 1,000 sq ft before planting, not after the grass is up.
The worked examples on this page were run through the same construction engine the calculator above uses on 29 October 2026, and every rate in the tables is quoted from the Extension page cited beside it.
Where this calculator stops
It converts an area and a rate into pounds. It will not tell you which grass to grow — that depends on your climate, your shade, and how much you water, and a Extension office for your state answers it better than a calculator can. It does not include the price of seed, because that moves with cultivar and season. And it does not account for germination percentage on the tag: if a bag tests at 85 % germination, the live seed in it is 15 % less than the weight suggests, which is the one adjustment worth making on top of the number this page gives you.
