How much overlap do I need for weed membrane?

The industry standard overlap for weed membrane is 150mm (6 inches). This prevents weeds from growing through the joins. For areas with aggressive weeds such as Japanese knotweed or horsetail, increase the overlap to 300mm. Always secure overlapping joins with fixing pins at 300mm centres along the join.

How many fixing pins do I need per square metre?

Use approximately 6 fixing pins per square metre for a secure installation. Place pins at all edges, overlaps and at regular intervals across the sheet. For windy or sloped areas, increase to 8-10 pins per m². Standard U-shaped membrane pins are 150mm (6 inch) long for most applications.

Should I use 1m or 2m wide weed membrane?

Use 2m wide membrane wherever possible — it means fewer joins and overlaps, which gives better weed suppression and uses less material. Use 1m wide rolls for narrow borders, paths under 1m, or areas with many curves where a narrower roll is easier to handle and wastes less.

What weight weed membrane should I use?

For most garden landscaping, use 100g/m² weed membrane. Under driveways and heavy traffic areas, use at least 125g/m² heavy-duty membrane. For flower beds where you want some water and air permeability, 50g/m² is fine. Always use a woven or needle-punched geotextile rather than thin plastic sheeting.

Do I need weed membrane under gravel?

Yes, weed membrane under gravel is strongly recommended. Without it, weeds will grow through within a season, and the gravel will gradually sink into the soil. Lay the membrane on level ground, pin it securely, and add gravel on top. Use our Gravel Calculator to work out how much gravel you need.

TradeCalcs

Weed Membrane Calculator — How Much Landscape Fabric Do I Need?

Calculate weed membrane rolls, overlap allowance and fixing pins for driveways, borders, paths and gravel areas.

Area Length

Length of the area to cover

Area Width

Width of the area to cover

Membrane Overlap

150mm standard, 300mm for heavy weeds

Roll Size

Choose roll width and length

Include fixing pins

6 pins per m² — secures membrane to the ground

Price Per Roll (optional)

Enter your supplier price for a cost estimate

How We Calculate This

Our weed membrane calculator works out how many strips of membrane you need to cover your area, accounting for the overlap between adjacent strips, then calculates the number of rolls to purchase and fixing pins required.

The formula

Strips needed = Area width ÷ (Roll width - Overlap) (rounded up)

Total linear metres = Strips × Area length

Rolls needed = Total linear metres ÷ Roll length (rounded up)

Fixing pins = Area (m²) × 6 (rounded up)

Recommended overlaps

Standard gardens: 150mm overlap
Heavy weed areas: 300mm overlap
Under driveways: 150-200mm overlap

Fixing pin guidance

Standard areas: 6 pins per m²
Sloped or windy areas: 8-10 pins per m²
Overlap joints: Every 300mm along the join

This calculation follows landscape industry standards for weed suppression membrane installation used by UK landscaping professionals.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Verify with your supplier.