Weed Barrier / Landscape Fabric Calculator

Landscape weed barrier (ground cloth / weed fabric) blocks sunlight to prevent weed germination while allowing water and air to pass through. Accurate coverage calculation prevents costly mid-project shortages.

Coverage formula:

Dividing bed area by roll area is the obvious way to do this and it is wrong, because fabric comes on a roll of a fixed width and you cannot stretch it sideways. What decides the answer is how many strips the bed takes:

Strips = Bed width ÷ (Roll width − 6 inch overlap), rounded up Linear feet = Strips × Bed length Rolls = Linear feet ÷ Roll length, rounded up

Run the strips along the longer side. That always gives you fewer of them, and fewer seams is both less fabric and fewer places for a weed to find its way up.

Overlap allowance: strips overlap 6 to 12 inches so weeds cannot come through the join. This calculator uses 6 inches, which is the usual figure and enough on a flat bed. Go to 12 on a slope, where the fabric shifts.

Worked example:

A garden bed 15 ft × 25 ft, using 3 ft × 100 ft rolls.

• Run the strips along the 25 ft side, so each strip is 25 ft long
• A 3 ft roll with 6 inches of overlap covers 2.5 ft of new ground per strip
• Strips: 15 ÷ 2.5 = 6 strips
• Linear feet: 6 × 25 = 150 ft
• Rolls: 150 ÷ 100 = 1.5 → buy 2 rolls, with 50 ft left over

Cut around existing shrubs rather than trying to subtract their area up front. You still need the fabric to run past them, and an X-cut with the flaps tucked under the mulch is what keeps weeds from following the stem up.

Weed barrier types and lifespans:

Mulch layer required on top: Weed barrier alone still allows weed seeds to germinate in surface dirt. Always top with 2–4 inches of mulch to suppress light and soil erosion.

Staple spacing: Use landscape fabric staples every 12 inches along edges and every 18 inches through the middle. In windy areas, reduce to 8–10 inches at all edges.