Grass seed rates vary more between species than most people expect — by a factor of fifteen across the common ones — because seed size differs so much. This calculator uses per-species rates rather than a single average, for either a new lawn from bare soil or an overseed of existing turf.
How to use it
- Enter the lawn area. For an awkward shape, break it into rectangles and add them up, or measure the whole plot and subtract the house, drive and beds.
- Choose your grass. If you are overseeding and do not know what is there, match the climate: cool-season grasses in the northern US, Canada and the UK; warm-season in the southern US and Australia.
- Say what you are doing. Bare soil takes the full establishment rate; existing turf takes the lower overseeding rate.
How it is calculated
pounds of seed = rate (lb per 1,000 sq ft) x (area / 1000)
The whole question is which rate. Rates come from
data/grass-seed-rates.ts. For the grasses Penn State's table covers, the new-lawn
figure is the midpoint of its published range and the result says so, with the range
itself in the table below. The note under the result explains anything particular
about that grass.
A worked example
A 5,000 square foot lawn, new, in tall fescue:
- Rate: 7 lb per 1,000 sq ft — the midpoint of Penn State's published 6 to 8
- Seed needed: 7 x (5,000 / 1,000) = 35 pounds
Overseeding the same lawn instead uses tall fescue's lower rate of 3.5 lb per 1,000 sq ft, so 17.5 pounds. Switch the species to Kentucky bluegrass and the new-lawn figure drops to 12.5 pounds, because bluegrass seed is so much smaller that a pound goes far further.
Pure live seed, and when the bag matters
The rates above are pounds of seed as sold, and they already assume normal, decent-quality seed — so with an ordinary bag, buy the weight the calculator gives. The purity and germination on the label matter when seed is poor: their product is the pure live seed (PLS) share, the part of the bag that can actually grow (PLS weight = bulk weight × purity × germination). Only a below-standard bag calls for an adjustment: buy rate ÷ (purity × germination) instead.
A 1,000 square foot patch of perennial ryegrass at 5 lb per 1,000 sq ft:
- Ordinary bag (95% purity, 85% germination — meets the standard): buy 5 lb. No adjustment.
- Poor bag (85% purity, 72% germination — Penn State's own below-standard example): PLS share = 0.85 × 0.72 = 61%. Bulk to buy = 5 ÷ 0.61 ≈ 8.2 lb.
Zoysiagrass is the exception: Arkansas publishes its 1–2 lb rate as pure live seed, so for zoysiagrass divide the rate by (purity × germination) whatever the bag — at 90% purity and 80% germination, 1.5 ÷ 0.72 ≈ 2.1 lb of bulk seed.
Seeding rates by grass type
| Grass | Season | New lawn, as published | Overseeding | Rate written for |
|---|---|---|---|---|
| Annual ryegrass | Cool | 9 lb | 6 lbEstimate: no extension source was found for the overseeding rate for Annual ryegrass, so it is a typical published value rather than a checked one. | New England (as a full cover); far lower where it is a temporary winter crop |
| Creeping bentgrass | Cool | 1 lb | 0.5 lbEstimate: no extension source was found for the overseeding rate for Creeping bentgrass, so it is a typical published value rather than a checked one. | Pennsylvania and New England, golf turf rather than home lawns |
| Fine fescue | Cool | 4 to 5 lb | 3 lbEstimate: no extension source was found for the overseeding rate for Fine fescue, so it is a typical published value rather than a checked one. | Pennsylvania and New England |
| Kentucky bluegrass | Cool | 2 to 3 lb | 2 lb | Pennsylvania, New York and Nebraska |
| Perennial ryegrass | Cool | 4 to 5 lb | 3.5 lb | Pennsylvania, New York and New England |
| Tall fescue | Cool | 6 to 8 lb | 3.5 lb | Pennsylvania, New York and Nebraska |
| Bahiagrass | Warm | 6 lb | 4 lbEstimate: no extension source was found for the overseeding rate for Bahiagrass, so it is a typical published value rather than a checked one. | North Carolina and Florida |
| Bermudagrass (hulled seed) | Warm | 1.5 lb | 1 lbEstimate: no extension source was found for the overseeding rate for Bermudagrass (hulled seed), so it is a typical published value rather than a checked one. | North Carolina and Florida |
| Buffalograss | Warm | 4 lb | 2 lbEstimate: no extension source was found for the overseeding rate for Buffalograss, so it is a typical published value rather than a checked one. | Colorado; Kansas publishes 1-2 for the same grass |
| Centipedegrass | Warm | 0.4 lb | 0.25 lbEstimate: no extension source was found for the overseeding rate for Centipedegrass, so it is a typical published value rather than a checked one. | North Carolina and Florida |
| Zoysiagrass | Warm | 1.5 lb PLS | 1 lb PLSEstimate: no extension source was found for the overseeding rate for Zoysiagrass, so it is a typical published value rather than a checked one. | Arkansas and North Carolina |
Tips and common mistakes
Sow half in one direction and half at right angles. A single pass always leaves stripes. Two passes crossing each other is the simplest way to get even coverage from a spreader or by hand.
Keep the surface damp, not the soil soaked. Germinating seed dies if the top half inch dries out even once. That usually means a light watering once or twice a day for two or three weeks, not a deep soak every few days.
Do not fertilise heavily at sowing. A starter fertilizer with phosphorus helps root development, but a nitrogen-heavy feed encourages the weeds that are competing with your seedlings.
Check the seed label for coating and filler. Some products are a mix of seed, inert matter and mulch, so a given weight contains less actual seed than a bag of pure seed. The percentages are on the label.
Buy fresh seed. Germination falls off after a couple of years in storage, and a bargain bag of old seed is not a bargain.