How Much Grass Seed per m2? Seeding Rates

To establish a new lawn, you generally need 25 to 30 grams of grass seed per square meter (approximately 2.5 to 3 pounds per 1,000 square feet). For overseeding an existing lawn, reduce that rate to 15 to 20 grams per square meter. This calculator estimates the total seed weight you need based on your lawn area and the seeding rate you choose.

Formula

The calculation is straightforward:

Total seed (g) = Length (m) × Width (m) × Seeding rate (g/m²)

Where:

• Length and Width are the dimensions of the lawn in meters.
• Seeding rate is the amount of seed per square meter, typically 25–30 g for a new lawn, 15–20 g for overseeding, and 40–50 g for patch repair.

The result is given in grams and kilograms. To convert to pounds, divide the total grams by 453.6.

Worked Example

Using the default values from the calculator:

1. Lawn length = 10 m, width = 5 m, so area = 10 × 5 = 50 m².
2. Seeding rate for a new lawn = 30 g/m².
3. Total seed = 50 × 30 = 1,500 g.
4. In kilograms: 1,500 ÷ 1,000 = 1.5 kg.

So for a 50 m² new lawn, you need about 1.5 kg of grass seed.

Why Seeding Rate Matters

Grass seed is sold by weight, but the number of seeds per gram varies widely by species. For example, perennial ryegrass has roughly 500 seeds per gram, while creeping bentgrass has over 4,000 seeds per gram. A rate that works for one species may be too sparse or too dense for another. The rates given here are general guidelines for common lawn mixes. Always check the seed label—many suppliers list a recommended rate for the specific blend, which may differ from the generic figure.

Using too little seed results in a thin, patchy lawn that weeds will quickly colonize. Using too much seed can cause overcrowding, where seedlings compete for light, water, and nutrients, leading to weak growth and increased disease risk. The goal is a dense but not suffocated stand.

How to Choose the Right Rate

Your situation determines the rate:

• New lawn: 25–30 g/m². This gives enough seed to form a thick turf without excessive competition.
• Overseeding: 15–20 g/m². You are adding seed to existing grass, so a lighter rate avoids smothering the current lawn.
• Patch repair: 40–50 g/m² for bare spots. Higher density helps fill in quickly, but you should rake the seed into the soil for good contact.
• Shaded areas: Increase the rate by about 25% because grass grows more slowly in shade and needs more seed to achieve the same density.

Also consider the time of year. In spring and autumn, germination is more reliable, so you can use the lower end of the range. In summer heat, use the higher end and water more frequently.

Common Mistakes and How to Avoid Them

Several errors can undermine your seeding efforts:

• Measuring the area incorrectly: Break the lawn into rectangles and circles, calculate each, and add them up. Do not estimate by eye—it is easy to be off by 20% or more.
• Ignoring the seed label: Some premium mixes have larger seeds or different recommended rates. The label is the most reliable source for that specific product.
• Applying unevenly: Divide the seed into two equal batches. Spread one batch walking in one direction, the other at a right angle. This gives even coverage.
• Not preparing the soil: Seed needs soil contact. Rake the surface, remove debris, and lightly roll or tamp after sowing.
• Forgetting to water: Keep the top 1–2 cm of soil consistently moist until germination. This may mean watering lightly once or twice a day in dry weather.

Cost and Buying Considerations

Grass seed is typically sold in 1 kg, 2 kg, 5 kg, or 10 kg bags. A 10 kg bag covers about 330–400 m² at the new-lawn rate. Buying a larger bag is usually more economical per kilogram, but you may not need that much. Compare prices per kilogram, not per bag. Also note that cheaper mixes often contain more filler or annual ryegrass, which germinates fast but dies after a season. For a permanent lawn, choose a mix with perennial species such as perennial ryegrass, tall fescue, or Kentucky bluegrass, depending on your climate.

If you are overseeding, you might also consider a slit seeder or a broadcast spreader. A drop spreader gives precise placement but is slower; a broadcast spreader is faster but can throw seed onto paths or flower beds. Calibrate your spreader before use—many are inaccurate out of the box.

Alternatives to Seeding

If you need an instant lawn, sod is the obvious alternative. Sod costs more but eliminates the germination period and the need for careful watering. Another option is hydroseeding, where a slurry of seed, mulch, and fertilizer is sprayed onto the soil. This is effective for slopes and large areas, but it is usually done by professionals. For small patches, you can use seed mats—pre-seeded biodegradable mats that hold moisture and protect the seed. These are convenient but more expensive per square meter than loose seed.

Frequently Asked Questions

Can I just throw grass seed on top of the soil?

Barely. Seed that is not in contact with soil will dry out quickly and may be eaten by birds. For best results, rake the area to loosen the top 1–2 cm, spread the seed, then rake again to mix it lightly, and roll or tamp. If the seed is visible on the surface, it is too exposed.

How long does grass seed take to germinate?

Most common lawn grasses germinate in 7 to 21 days, depending on species and soil temperature. Perennial ryegrass can appear in as little as 5–7 days, while Kentucky bluegrass may take 14–21 days. Keep the soil moist but not waterlogged during this period.

Should I use more seed if I have poor soil?

No. Poor soil limits growth regardless of seed density. Instead, improve the soil by adding compost or topsoil before seeding. Using more seed will only create competition for scarce nutrients. Test your soil pH and adjust if needed—most grasses prefer a pH between 6.0 and 7.0.

What is the best time of year to sow grass seed?

In cool climates, late summer to early autumn is ideal because the soil is warm, and the air is cooler, reducing water stress. Spring is the second-best option. In warm climates, late spring to early summer works better. Avoid sowing in the heat of summer unless you can water consistently.

How do I know if I am overseeding or starting a new lawn?

If you have less than 50% grass cover, it is usually better to renovate completely—kill the existing vegetation, prepare the soil, and seed at the new-lawn rate. If you have more than 50% cover but it is thin, overseed at the lighter rate. Overseeding into a lawn with lots of weeds will not fix the weed problem; address weeds first.

Related

• Aeration Blower Sizing Calculation: A Practical Guide
• Aeration Tank Design Calculation: Key Steps
• Overseeding Calculator: Grass Seed for an Existing Lawn

in l | Lawn length | m | 10 | 0 | 1000
in w | Lawn width | m | 5 | 0 | 1000
sel r | Seeding rate | New lawn=30, Overseeding=15, Patch repair=50
out g | Total seed | g | l * w * r | 0
out kg | Total seed | kg | l * w * r / 1000 | 2