Grass Seed Calculator per m² — Exact Quantity by Type & Purpose
Getting the seed rate right is the single most important step in lawn establishment. Too little seed leaves bare patches and invites weeds; too much wastes money and causes seedling competition. Rates vary widely by grass species — bermuda and bent grass need only 6–10 g/m², while premium ryegrass mixes require 35–40 g/m² for a new lawn. Select your grass type and purpose below to get the exact quantity in grams or kilograms.
For a new lawn, grass seed rates range from 10 g/m² (bermuda, bent grass) up to 40 g/m² (premium ryegrass-fescue mix). The most common species — perennial ryegrass and fine fescue — need 35 g/m² for a new lawn and 20 g/m² for overseeding. Formula: Seed (g) = Area (m²) × Seeding rate (g/m²). Always buy 10% extra to cover uneven spreading.
When to use this calculator
- Homeowner planning a new lawn from bare soil and wants to buy exactly the right number of seed bags
- Gardener overseeding thin or patchy areas in autumn or spring without wasting expensive seed
- Landscaping contractor estimating seed quantities for a client quote
- Sports turf manager calculating seed requirements for pitch renovation
Example: 80 m² garden lawn with perennial ryegrass (new lawn)
- Lawn area: 80 m²
- Grass type: Perennial ryegrass — New lawn
- Seeding rate: 35 g/m²
- Total seed: 80 × 35 = 2,800 g = 2.80 kg
- Recommended purchase (+ 10% buffer): 2.80 × 1.10 = 3.08 kg → buy two 2 kg bags
How it works
2 min readHow to Calculate Grass Seed Quantity
The formula is simple:
> Seed (g) = Area (m²) × Seeding rate (g/m²)
The seeding rate is the critical variable — it differs widely by grass species because seed size, germination density, and target sward thickness all vary.
Step-by-Step
1. Measure your lawn area in m² (length × width for a rectangle; break irregular shapes into sections).
2. Identify your grass type and purpose (new lawn or overseeding).
3. Multiply area by the rate from the table below.
4. Add 10% to your total to account for uneven hand-spreading and overlap.
Seeding Rate Table — All Major Grass Types
| Grass Type | New Lawn (g/m²) | Overseeding (g/m²) | Notes |
|---|---|---|---|
| Premium mix (rye + fescue) | 40 | 25 | Richest sward, best wear tolerance |
| Perennial ryegrass | 35 | 20 | Most popular cool-season species |
| Fine fescue mix | 35 | 20 | Shade-tolerant, low-maintenance |
| Tall fescue | 25 | 15 | Deep-rooted, drought-resistant |
| Bahia grass | 30 | 18 | Warm-season, good for sandy soils |
| Kentucky bluegrass | 20 | 12 | Dense, fine-textured turf |
| Bermuda grass | 10 | 6 | Warm-season, very small seeds |
| Bent grass | 10 | 6 | Used for golf greens, fine texture |
Quick Reference: Common Lawn Sizes
| Lawn Area | Ryegrass / Fescue (new, 35 g/m²) | Kentucky Bluegrass (new, 20 g/m²) | Bermuda (new, 10 g/m²) |
|---|---|---|---|
| 20 m² | 700 g (0.70 kg) | 400 g | 200 g |
| 50 m² | 1,750 g (1.75 kg) | 1,000 g | 500 g |
| 100 m² | 3,500 g (3.50 kg) | 2,000 g (2.0 kg) | 1,000 g (1.0 kg) |
| 200 m² | 7,000 g (7.0 kg) | 4,000 g (4.0 kg) | 2,000 g (2.0 kg) |
| 500 m² | 17,500 g (17.5 kg) | 10,000 g (10.0 kg) | 5,000 g (5.0 kg) |
Add 10% to all values before purchasing.
Sources: Lawnsmith (UK), The Grass People, AHDB Grassland Reseeding Guide, Cornell University Turfgrass Seeding Rates.
Why Overseeding Uses Less Seed
When overseeding an existing lawn, the established grass provides competition and shading. Using the full new-lawn rate would cause seedling overcrowding. The lower overseeding rate (roughly 55–60% of the new-lawn rate) gives new seed room to germinate without starving existing turf.
Why Bermuda and Bent Grass Need Less Seed
Bermuda and bent grass have extremely small, light seeds with a very high seed count per gram. A much lower weight achieves the same germination density as a heavier rate of larger-seeded species like tall fescue.
Tips for Accurate Application
Frequently asked questions
How much grass seed do I need per square meter for a new lawn?
It depends on the grass species. Perennial ryegrass and fine fescue mixes need 35 g/m²; tall fescue needs 25 g/m²; Kentucky bluegrass needs 20 g/m²; bermuda and bent grass need only 10 g/m². Premium ryegrass-fescue blends are typically applied at 40 g/m². Always add 10% to your total for uneven spreading.
How much seed do I need to overseed an existing lawn?
Overseeding rates are roughly 55–60% of new-lawn rates. Perennial ryegrass and fescue mixes need 20 g/m²; tall fescue 15 g/m²; Kentucky bluegrass 12 g/m²; bermuda 6 g/m². Using the full new-lawn rate when overseeding causes overcrowding and actually reduces germination success.
How do I calculate grass seed for an irregular lawn shape?
Break the area into rectangles and triangles, measure each, and add together. For curves or kidney shapes, divide into 1 m-wide strips and sum the lengths. Alternatively, measure the bounding rectangle and multiply by 0.8 as a correction for curved edges. Then enter the total m² into the calculator above.
Why do different grass types have different seed rates?
Seed size varies enormously between species. Bent grass seeds number roughly 12,000–15,000 per gram, so 10 g/m² provides millions of seeds. Tall fescue seeds are much larger (around 450–550 per gram), so you need more weight to achieve the same seed density. The calculator accounts for this automatically.
Should I buy more seed than the calculator recommends?
Yes — always add 10% to the calculated amount. Hand spreading and rotary spreaders apply seed unevenly, and a buffer ensures you don't run short. Running out halfway and reseeding a week later causes visible stripes in the finished lawn. The calculator shows both the exact amount and the recommended purchase quantity.
When is the best time of year to sow grass seed?
Cool-season grasses (ryegrass, fescue, bluegrass, bent grass) germinate best in spring (March–May) or early autumn (August–September) when soil temperature is 8–15°C. Warm-season grasses (bermuda, bahia) need soil temperatures above 18°C, so late spring to early summer is optimal. Autumn sowing for cool-season grasses has the advantage of less weed competition.
How many bags of grass seed do I need to buy?
Divide your buffered total by the bag size. Example: if the calculator says you need 3.1 kg (after the 10% buffer), and bags are sold in 2 kg units, 3.1 ÷ 2 = 1.55 → buy 2 bags. Common bag sizes are 500 g, 1 kg, 2 kg, and 5 kg. It's always better to have one small bag left over than to run short.
What happens if I use too much grass seed?
Excessive seeding causes overcrowding: seedlings compete for water, nutrients, and light, resulting in weak, spindly growth and higher disease risk (especially damping-off fungus). More seed does not mean faster or thicker establishment — staying within the recommended rate gives each seedling room to develop properly.
Is bermuda grass seed rate lower because it spreads vegetatively?
Partly. Bermuda grass spreads by stolons and rhizomes after establishment, so initial seed density is less critical than for bunch-type grasses. Additionally, bermuda seeds are very small (high count per gram), so a low weight still achieves adequate soil coverage. Use 10 g/m² for new lawns and 6 g/m² for overseeding.
Can I use this calculator for sports fields or golf courses?
Yes for sports pitches — enter the area in m² and select the appropriate grass type (bent grass for golf greens, ryegrass or fescue for football and rugby). The seeding rates are standard agronomic figures used by professional turf managers. For large areas (>5,000 m²) consult a turf agronomist for species blends and drilling vs broadcast seeding.