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

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 = 1 + ceil((Area width - Roll width) ÷ (Roll width - Overlap))

The first strip is laid full width; only the strips after it lose the overlap to their neighbour. If a single roll already spans the width, you need just 1 strip.

Total linear metres = Strips × Area length

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

Fixing pins = Area (m²) × pins per m² (default 6, rounded up)

Recommended overlaps

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

Fixing pin guidance

Pin density is a rule of thumb, not a fixed standard — it varies with ground conditions and exposure. The calculator defaults to a conservative 6 per m² so you do not under-order; you can lower it in the advanced options.

• Flat ground: roughly 2–4 pins per m²
• Sloped, curved or windy areas: about 5–6 pins per m²
• Edges & overlap joints: always pin at around 300mm centres

Overlap and pinning figures follow common UK weed-membrane supplier and installer guidance; always follow the manufacturer’s instructions for your specific fabric.