How Much Grass Seed Do I Need Per m²?
This calculator tells you exactly how many grams (or kilograms) of grass seed you need to cover a given area in square metres. The core formula is: Total Seed (g) = Area (m²) × Seeding Rate (g/m²). Seeding rates vary by grass species — from as low as 10–15 g/m² for Bermudagrass to 35–50 g/m² for tall fescue blends — so getting the math right prevents costly overseeding or patchy, thin coverage.
Grass seed requirements per m²: **Ryegrass (perennial): 30–40 g/m²**, **Tall Fescue: 35–50 g/m²**, **Seed Blend: 35 g/m²**, **Bermudagrass: 10–15 g/m²**. For 100 m² with a standard blend: 100 × 35 = **3.5 kg of seed**. For overseeding into existing turf, use 50% of the new-seeding rate. Formula: Seed (g) = Area (m²) × Seeding Rate (g/m²).
When to use this calculator
- Establishing a brand-new residential lawn of 250 m² with a tall fescue blend at 35 g/m² — calculate 8.75 kg before buying bags at the garden centre.
- Overseeding a worn sports field of 1,200 m² with perennial ryegrass at 18 g/m² (overseeding rate) — budget for 21.6 kg of seed.
- Repairing bare patches totalling 18 m² in an existing lawn after drought, using 35 g/m² to buy only the small quantity needed.
- Planning a low-maintenance meadow of 500 m² with a fine fescue mix at 15 g/m² — 7.5 kg is sufficient.
- Seeding a rooftop garden of 80 m² with a shade-tolerant grass mix (25 g/m²) — calculating 2 kg to fit a tight contractor budget.
Example: 100 m² lawn with a seed blend
- Area: 100 m²
- Grass type: Seed Blend → rate 35 g/m²
- Total: 100 × 35 = 3,500 g
How it works
2 min readHow It's Calculated
The fundamental formula is:
Total Seed (g) = Area (m²) × Seeding Rate (g/m²)
Total Seed (kg) = Total Seed (g) ÷ 1,000
For overseeding into existing turf:
Overseeding Rate = New-Seeding Rate × 50%The seeding rate is the most critical variable and depends on species, whether you are doing a new seeding or overseeding, and soil conditions.
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Grass Seed Rate Table (per m²)
| Grass Type | New Lawn (g/m²) | Overseeding (g/m²) | Season | Notes |
|---|---|---|---|---|
| Perennial Ryegrass | 30–40 | 15–20 | Cool | Fast germination (5–10 days) |
| Annual Ryegrass | 30–40 | 20–25 | Cool | Cheap, short-lived cover |
| Tall Fescue | 35–50 | 18–25 | Cool | Heat & drought tolerant |
| Fine Fescue (blend) | 12–18 | 8–12 | Cool | Shade tolerant |
| Kentucky Bluegrass | 15–20 | 8–12 | Cool | Slow to establish (3–6 months) |
| Bermudagrass | 10–15 | 5–8 | Warm | Full sun, very drought tolerant |
| Zoysiagrass | 8–12 | 5–8 | Warm | Low maintenance once established |
| Buffalograss | 20–30 | 10–15 | Warm | Native, drought tolerant |
> Sources: USDA NRCS Plant Materials Program; Penn State Extension; University of California ANR.
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How much seed for common areas?
| Area | Ryegrass (35 g/m²) | Tall Fescue (40 g/m²) | Seed Blend (35 g/m²) | Bermuda (12 g/m²) |
|---|---|---|---|---|
| 25 m² | 875 g | 1.0 kg | 875 g | 300 g |
| 50 m² | 1.75 kg | 2.0 kg | 1.75 kg | 600 g |
| 100 m² | 3.5 kg | 4.0 kg | 3.5 kg | 1.2 kg |
| 200 m² | 7.0 kg | 8.0 kg | 7.0 kg | 2.4 kg |
| 500 m² | 17.5 kg | 20 kg | 17.5 kg | 6.0 kg |
| 1,000 m² | 35 kg | 40 kg | 35 kg | 12 kg |
> For overseeding, halve these quantities.
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Worked Examples
New residential backyard (Tall Fescue)
Overseeding a sports field (Perennial Ryegrass)
Shaded side yard (Fine Fescue)
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Common Mistakes
1. Using the full new-seeding rate for overseeding — only use 40–70% of the new rate into existing turf.
2. Ignoring germination percentage on the bag — a bag at 85% germination means 15% of seeds won't sprout. A high-quality turf seed should show ≥95% purity and ≥85% germination.
3. Not accounting for slopes — a 20° slope adds ~6% actual surface area vs. the flat measurement. Always add 10–12% buffer.
4. Sowing too deep — most grass seeds need 3–6 mm of coverage (¼ inch max). Burying deeper dramatically reduces germination.
5. Seeding in summer — for cool-season grasses, soil temps above 25°C inhibit germination. Optimal window: late summer to early autumn.
Frequently asked questions
How much grass seed do I need per square metre?
It depends on the species: Ryegrass: 30–40 g/m², Tall Fescue: 35–50 g/m², Seed Blend: ~35 g/m², Bermudagrass: 10–15 g/m². For overseeding into existing lawn, use 50% of the new-seeding rate. Always check the seeding rate printed on the seed bag.
How many kg of grass seed for 100 m²?
With a standard seed blend (35 g/m²): 3.5 kg. With ryegrass (35 g/m²): 3.5 kg. With tall fescue (40 g/m²): 4 kg. With Bermudagrass (12 g/m²): 1.2 kg. If overseeding, halve these quantities.
Is the overseeding rate different from the new-seeding rate?
Yes — overseeding into existing turf uses only 40–70% of the new-seeding rate. For example, if Tall Fescue is seeded at 35 g/m² for a new lawn, overseeding into thin turf needs only 15–25 g/m². The existing canopy competes with seedlings, making it wasteful to apply the full new rate.
What soil temperature do I need for grass seed to germinate?
Cool-season grasses (Bluegrass, Fescues, Ryegrass) germinate best at soil temperatures of 10–18°C (50–65°F), typically autumn or early spring. Warm-season grasses (Bermuda, Zoysia, Buffalograss) need soil temps above 18°C (65°F), generally late spring through summer.
When is the best time to seed a lawn?
For cool-season grasses, late summer to early autumn (August–October in the Northern Hemisphere; March–May in the Southern Hemisphere) is optimal: soil is still warm but air temperatures are falling, reducing heat stress on seedlings. Spring seeding is a secondary option but competes with weed germination. Avoid mid-summer for cool-season species.
Why should I add a 10–15% buffer to my seed calculation?
Several real-world factors reduce effective coverage: slopes increase true surface area, uneven soil causes seed to accumulate in depressions, birds and wind carry seed away, and hand-spreading is rarely perfectly uniform. A 12% buffer is a standard industry recommendation to avoid running short mid-project.
How long does grass seed take to establish?
Germination timelines: Perennial Ryegrass: 5–10 days (fastest). Tall Fescue: 7–12 days. Kentucky Bluegrass: 14–30 days (slowest). Full establishment — turf able to handle foot traffic — takes 6–10 weeks for ryegrass/fescue and 3–6 months for Kentucky Bluegrass. Avoid mowing until grass reaches 7–10 cm.
How do I read a grass seed label to verify quality?
A high-quality turf seed label shows: (1) pure seed ≥95%, (2) germination ≥85%, (3) weed seed <0.5%, (4) inert matter <5%. Multiply purity × germination to get the effective seed fraction — e.g., 97% × 88% = 85.4% of the bag weight is viable seed. Labels with high inert matter percentages mean you're paying for filler.
Does seed depth affect how much seed I should buy?
Seed depth affects germination rate, not quantity. Most grass seeds should be placed at 3–6 mm depth. Poor seed-to-soil contact — not insufficient quantity — is the most common cause of low germination in home lawn projects. Use a slit-seeder or light raking after broadcast spreading to ensure contact.