How the calculation works

Seed needed is the lawn area multiplied by a seeding rate.

US rates are given in pounds per 1,000 sq ft, so seed (lb) = area (sq ft) ÷ 1,000 × rate.
Metric rates are in grams per square metre, so seed (g) = area (m²) × rate. A rate of 1 lb per 1,000 sq ft is 4.88 g/m².
Which rate: extension services don't all agree, so each grass has a range that runs from the lowest to the highest rate in the sources below. The calculator uses the midpoint unless you choose the low or high end.
Overseeding: NC State says a 25 to 50 percent lower rate may be right when seeding into an existing lawn. So the overseeding range runs from half the lowest new-lawn rate to three-quarters of the highest. For UK mixes it uses 15–25 g/m², from the RHS (its usual packet rate for reseeding patches) and Johnsons (25 g/m² for overseeding).
Bags: seed needed ÷ bag size, rounded up to a whole bag.

Worked example

A new 5,000 sq ft tall fescue lawn. The sources' rates for tall fescue run from 5 to 10 lb per 1,000 sq ft, so the midpoint is 7.5 lb (36.6 g/m²). Seed needed = 5,000 ÷ 1,000 × 7.5 = 37.5 lb (17.01 kg). In 20 lb bags that is 2 bags (40 lb), with 2.5 lb to spare, and one bag covers about 2,667 sq ft. At the low end of the range you would need 25 lb, and at the high end 50 lb.

To overseed the same lawn instead, the range is 2.5 to 7.5 lb per 1,000 sq ft (half of 5 and three-quarters of 10). At the 5 lb midpoint you need 25 lb.

In metric, a new 60 m² lawn sown with a UK lawn seed mix at the midpoint of 35–50 g/m² (42.5 g/m²) needs 60 × 42.5 = 2,550 g, or 2.55 kg: two 1.5 kg boxes. To thicken the same lawn at 20 g/m² (the midpoint of 15–25) you need 1.2 kg, which is one box.

Seeding rates by grass

Rates are in pounds per 1,000 sq ft (lb), or grams per square metre (g/m²) for the UK mix. The last column shows each source's own figure, so you can see where they differ. Ohio State's rates are the highest for tall fescue and ryegrass, while NC State and UGA give the lowest rates for tall fescue.

Grass	New lawn	Overseeding	Published new-lawn rates
Kentucky bluegrass	1–3 lb	0.5–2.25 lb	Purdue 1.5–2; Penn State 2–3; NC State 1–2; UGA 1–3; Ohio State 2–3
Tall fescue	5–10 lb	2.5–7.5 lb	Purdue 6–9; Penn State 6–8; NC State 6; UGA 5–6; Ohio State 8–10
Perennial ryegrass	4–8 lb	2–6 lb	Penn State 4–5; Ohio State 7–8
Fine fescues	3–6 lb	1.5–4.5 lb	Penn State 4–5; UGA 4–5; Ohio State 3–6
Kentucky bluegrass + perennial ryegrass	2–4 lb	1–3 lb	Purdue 3–4; Penn State 2–3; NC State 2.5
Kentucky bluegrass + fine fescue	3–5 lb	1.5–3.75 lb	Purdue 4–5; NC State 3
Bluegrass + fine fescue + ryegrass	3–4 lb	1.5–3 lb	Penn State 3–4
Tall fescue + Kentucky bluegrass	6 lb	3–4.5 lb	NC State 6
Bermudagrass, hulled seed	1–2 lb	0.5–1.5 lb	NC State 1–2; UGA 1–2
Bermudagrass, unhulled seed	3–6 lb	1.5–4.5 lb	UGA 3–6
Zoysiagrass (seeded types)	1–3 lb	0.5–2.25 lb	NC State 1–2; UGA 1–3
Centipedegrass	0.25–1 lb	0.13–0.75 lb	NC State 0.25–0.5; UGA 0.25–1
Buffalograss (burs)	1–2 lb	0.5–1.5 lb	Nebraska 1–2; Kansas State 1.5–2
General lawn seed mix (UK)	35–50 g/m²	15–25 g/m²	Johnsons (DLF) 35–50. Overseeding: RHS 15–25; Johnsons (DLF) 25

Overseeding rates are worked out with NC State's 25–50% reduction, except for the UK mix, which has its own published rates.

When to sow

Cool-season grasses (bluegrass, fescues, ryegrass and their mixes)

Cool-season grass: sow in late summer to early fall. Purdue's best window is August 15 to September 15 in northern Indiana and September 1 to 30 in southern Indiana, and it says to seed as early in the window as you can. The window is later in the South: NC State gives September 1 to October 1 for tall fescue in the piedmont, and UGA September to October. Spring is the second choice, because seedlings have less time to root before summer heat and drought (NC State, Penn State): Penn State lists mid to late spring, NC State mid-February to early March in the piedmont, and UGA late February through March. Summer sowings suffer from heat, drought and disease (Penn State).

Warm-season grasses (bermudagrass, zoysiagrass, centipedegrass, buffalograss)

Warm-season grass: sow in late spring to early summer. UGA advises seeding once the soil 4 inches down is consistently 65°F and rising, usually mid to late spring, and no later than early to mid-August so seedlings can root before frost. NC State gives April to July for bermudagrass and zoysiagrass in the piedmont. Buffalograss seed will not germinate until the soil reaches 60°F, usually after mid to late May in Nebraska, where June 1 is a good target (University of Nebraska).

UK lawns

Sow in early autumn or mid-spring. The RHS recommends autumn (September to November) or mid-spring (March to April). Early autumn is the better choice if you have one, because the seedlings can establish before the first hard frosts.

Tips for a good result

Check the seed label. Purdue looks for germination above 85% and a germination test dated within the last 9 months. Penn State explains that seed with low purity or germination has to be sown more heavily to give the same lawn, so a cheap bag can cost more in the end.
More is not better. NC State and Penn State both warn that very heavy seeding gives weak or overcrowded stands that are more prone to disease.
Coated seed carries extra weight, so NC State notes it needs a higher rate. Follow the label for coated products.
Spread it evenly. Sow half the seed walking one way and half at right angles (Purdue, UGA and the RHS all suggest this), then rake lightly so the seed is in contact with the soil.
Birds: the RHS suggests covering new seed with horticultural fleece, or sowing 50% more seed to allow for losses.
Bare patches: the RHS gives about 15–25 g/m² for reseeding a bare patch, while Johnsons suggests its full new-lawn rate of 35–50 g/m². NC State's advice points the same way as Johnsons: use the new-lawn rate on bare soil, and the lower rate only where grass is still growing.
Winter color on bermudagrass (sowing ryegrass into it, as NC State notes some homeowners do) is a different job from thickening a lawn. UGA lists annual and perennial ryegrass for this kind of overseeding at 5–10 lb per 1,000 sq ft, sown September to November. The overseeding option here is for thickening a lawn with its own grass.

Common questions

How much grass seed do I need per 1,000 square feet?: It depends on the grass. Across the extension services used here, new-lawn rates per 1,000 sq ft are: Kentucky bluegrass 1–3 lb, tall fescue 5–10 lb, perennial ryegrass 4–8 lb, fine fescues 3–6 lb, hulled bermudagrass 1–2 lb, zoysiagrass 1–3 lb, centipedegrass 0.25–1 lb and buffalograss burs 1–2 lb. The calculator uses the middle of each range unless you choose the low or high end.
How much seed do I need to overseed a lawn?: Less than for a new lawn. NC State says a rate 25 to 50 percent lower may be right when seeding into existing grass. For tall fescue that gives 2.5–7.5 lb per 1,000 sq ft, and at the 5 lb midpoint a 5,000 sq ft lawn needs 25 lb. UGA's own figure for thin tall fescue is a little lower: 2–6 lb, or the share of the lawn that has thinned out times its 6 lb new-lawn rate (3 lb if half is lost). Where the soil is bare, use the "New lawn" rate instead.
How much lawn does a 1.5 kg box of grass seed cover?: At the 35–50 g/m² Johnsons gives for a new lawn, a 1.5 kg box covers 30–43 m², or about 35 m² at the 42.5 g/m² midpoint. For overseeding at 15–25 g/m² it covers 60–100 m², or 75 m² at 20 g/m². Check the box too: the RHS points out that the rate varies by mix.
Why do the sources give different seeding rates?: Each extension service writes for its own state, and they don't all agree. For tall fescue, UGA recommends 5–6 lb per 1,000 sq ft and NC State 6 lb, while Ohio State gives 8–10 lb. NC State also warns that heavier seeding gives weak, thin stands that suffer more from disease and heat. If you live in the South, the NC State and UGA rates are the ones written for your area.
Can I grow St. Augustinegrass from seed?: No. NC State notes that St. Augustinegrass seed is not available, so it is planted as sod, plugs or sprigs. Most fine-textured hybrid bermudagrasses, and the zoysiagrass cultivars Meyer and Emerald, are planted that way too. Pick St. Augustinegrass or hybrid bermudagrass in the calculator to see when to plant.

Sources

Last checked and updated: October 31, 2026.