How the fabric calculator works
- Strips across the width. The first strip covers the roll width. Each extra strip covers the roll width minus the seam overlap. A bed 8 ft wide with 3 ft fabric and 6 inch seams needs 1 + (8 − 3) ÷ 2.5 = 3 strips.
- Strip length. The bed length plus extra at each end to tuck into the edging. A 30 ft bed with 6 inches each end is 31 ft.
- Rolls. Each roll yields as many whole strips as fit along its length. Leftovers shorter than a strip don’t count.
Worked example
A 30 × 8 ft bed, 6 inch seams, 6 inches extra at each end:
- 3 ft × 50 ft rolls: 3 strips of 31 ft. Each roll gives one strip, so you need 3 rolls, with 19 ft left over on each.
- 4 ft × 100 ft roll: (8 − 4) ÷ 3.5 = 1.14, so 1 + 2 = 3 strips of 31 ft = 93 ft. One roll gives three strips: 1 roll.
The second option covers the same bed with one roll instead of three, which is why it’s worth trying a couple of roll sizes in the calculator before you buy.
Fabric needed for common beds
With 6 inch seams and 6 inches at each end:
| Bed | Strips (3 ft fabric) | Linear ft (3 ft) | Strips (4 ft fabric) | Linear ft (4 ft) |
|---|---|---|---|---|
| 20 × 3 ft | 1 | 21 | 1 | 21 |
| 20 × 6 ft | 3 | 63 | 2 | 42 |
| 30 × 4 ft | 2 | 62 | 1 | 31 |
| 40 × 5 ft | 2 | 82 | 2 | 82 |
| 50 × 8 ft | 3 | 153 | 3 | 153 |
Take the linear feet to the store and check how many whole strips each roll length gives.
When fabric is worth it under mulch
Landscape fabric blocks weeds from below, but it isn’t always the right call:
- Good places for fabric: under rubber mulch (so it doesn’t work into the soil), under paths of wood chips, under play areas, and in beds you won’t replant.
- Places many gardeners skip it: planted beds with wood mulch. The mulch breaks down into a thin layer of soil on top of the fabric, and weed seeds that land there root into it. Fabric also makes it harder to add plants later. Cardboard under mulch is a common alternative that breaks down over a season or two.
Laying landscape fabric
- Clear weeds and grass, rake the soil smooth and remove sharp stones.
- Roll out the first strip along the bed and pin it at the ends.
- Lay the next strip with the agreed overlap, then pin along the seam.
- Tuck the ends and edges down into the edging or a shallow trench.
- Cut an X where each plant goes and fold the flaps under.
- Cover with mulch. Use the mulch calculator for the quantity; with fabric underneath, 2–3 inches of most mulches is enough. For rubber mulch, 1.5–2 inches; see the rubber mulch calculator.
Measuring for fabric
Measure the length and the widest width of the bed. For curved beds, use the widest point so the fabric covers the bulges, then trim the excess. The measuring guide covers odd-shaped beds.
Roll sizes vary by brand and store. Common widths include 3, 4 and 6 ft, and lengths from 50 ft up. Check the label and set the calculator to match.
Questions people ask
- How do I calculate how much landscape fabric I need?
- Work out how many strips cover the width: the first strip covers the roll width, and each extra strip adds the roll width minus the seam overlap. Multiply strips by the bed length plus the extra at each end for linear feet, then see how many whole strips each roll gives.
- How much should landscape fabric overlap?
- Overlap seams by about 6 to 12 inches, more on slopes or with aggressive weeds, and pin the seams. Follow the fabric maker's instructions if they differ.
- Should I put landscape fabric under mulch?
- It depends. Fabric works well under rubber mulch, under paths and in areas you won't replant. In planted beds with wood mulch, many gardeners skip it, because the mulch breaks down on top of the fabric and weeds root into that layer anyway.
- How many staples do I need for landscape fabric?
- Pin every seam and edge. Spacing depends on the fabric, wind and slope; use the spacing on the fabric or staple package, and add extra pins on slopes and around cut-outs for plants.
- Why does the calculator say I need more rolls than the area suggests?
- Because strips can't be pieced together from leftover ends without extra overlap. If a roll is 50 feet long and each strip is 31 feet, each roll only gives one usable strip.