Grass Seed Calculator: How Much Seed per m² for a Lawn

Work out the kilos of grass seed and bags of 1, 5 or 10 kg for your area: new lawn at about 35 g/m², overseeding at 20 g/m², fertiliser included.

How much grass seed do you need per square metre?

To establish a lawn, plan on about 35 g of seed per m² (30 to 40 g depending on the mix) and 20 g/m² for overseeding. A 200 m² lawn therefore needs about 7 kg of seed, i.e. 2 bags of 5 kg. These rates are seed producers’ recommendations: the instructions on the bag take precedence.

The formula

Seed (kg) = area (m²) × rate (g/m²) ÷ 1,000. Number of bags = kg needed ÷ bag weight, rounded up for each size. Starter fertiliser (kg) = area × rate.

Worked example: 200 m²

  • New lawn at 35 g/m²: 200 × 35 ÷ 1,000 = 7 kg, i.e. 7 bags of 1 kg, 2 bags of 5 kg or 1 bag of 10 kg
  • Overseeding at 20 g/m²: 4 kg
  • Starter fertiliser at 30 g/m²: 6 kg

The tool’s default rates

  • All-purpose lawn: 35 g/m² for a new lawn, 20 g/m² for overseeding
  • Sports or shade lawn: 40 and 25 g/m²
  • Hard-wearing low-maintenance lawn: 30 and 15 g/m²

These values are recommendations, not a rule. Seed producers’ sheets range from 20 to 30 g/m² for a new lawn and 10 to 30 g/m² for repair or overseeding. For a new lawn the tool uses a denser rate (30 to 40 g/m²); for overseeding it stays within the range. Every rate can be changed: lower it if your mix’s instructions say so.

Limits

The exact rate depends on the mix, the soil and the sowing date; the instructions on the bag take precedence. Sow in two crossing passes for an even spread.

Sources and dates: DCM Activo technical sheet (new lawn 2 to 3 kg per 100 m², overseeding 1 to 2 kg per 100 m²); DLF Turfline overseeding technical sheet (25 to 30 g/m²); the SEMAE guide Petit guide du tapis vert (May 2023) gives no figure. Starter fertiliser at 30 g/m²: indicative value, not verified (checked on 14 October 2026).

Frequently Asked Questions

How many kilos of grass seed for 100 m²?

For a new lawn at 35 g/m², you need 3.5 kg of seed per 100 m². For simple overseeding at 20 g/m², plan on 2 kg. A 5 kg bag therefore covers about 140 m² for a new lawn.

What seed rate should I use to overseed a lawn?

For overseeding, use about 15 to 25 g/m², roughly half of a new sowing (30 to 40 g/m²). Rake and aerate the soil first, then water regularly until the seed has germinated.

Do I need a starter fertiliser when sowing a lawn?

A phosphorus-rich starter fertiliser helps young seedlings root. Use 20 to 40 g/m² at sowing, i.e. 6 kg for 200 m² at 30 g/m². Stick to the manufacturer’s rate so you do not scorch the seedlings.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

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