Example: a 30 × 10 ft bed
Area is 300 ft², approximately 27.871 m². Suppose a reviewed layout gives 130 ft² of net usable coverage per roll after seams. Add an illustrative 10% for other cuts: 300 × 1.10 = 330 ft². Then 330 ÷ 130 = 2.5385, rounded to three rolls. The 10% does not include seam loss already removed from coverage.
Map the bed before choosing roll width
Split an irregular bed into measured areas, keeping its narrow sections and curves visible. A simple length-times-average-width estimate is useful early, but a strip sketch is more informative when you must buy rolls. Mark permanent obstructions and the areas around established plants.
Measure the intended treatment area rather than the entire garden plot. Paths and planted beds may use different products or details. The fabric quantity does not determine whether a particular fabric is suitable for the location; that comes from the landscape plan and product guidance.
Use the selected product’s seam instructions
DeWitt publishes a fabric installation guide covering seams and fixing. Use the instructions for your selected product and application when drawing overlapping strips. Do not assume a seam dimension from another fabric or a different use.
For a chosen overlap, each additional strip contributes less coverage width than the full roll width. Check the first and last strips separately because the boundaries can differ from internal seams. A blanket percentage can approximate material loss, but it does not prove that the proposed widths cover the bed.
Keep one clear basis in the calculator
One approach is to enter the documented net coverage of a roll after the expected seam treatment, then reserve waste only for additional cuts and handling. Another is to use gross roll area and an allowance derived from the actual layout. Write down which approach you used so a later revision remains understandable.
When entering net coverage, do not add the same seam loss again. Plant slits, irregular edges and damaged pieces are separate from the seams already allowed for. Avoid counting every plant opening as reusable material; a slit or shaped cut often does not produce an offcut that can cover another gap.
Finish the purchasing list
Divide the adjusted demand by usable roll coverage and round up, then compare that count with the strip sketch. Long continuous runs may need more usable length than an area-only result suggests. Credit remnants only when their width and length match a known remaining section.
Anchors, edging and the material placed above the fabric are separate quantities. A roll count does not calculate them. Keep those items beside the fabric line so the order reflects the complete planned scope without treating the fabric as a substitute for drainage or maintenance decisions.
Do it in order
- Sketch the treated bed and proposed strip direction.
- Confirm seam treatment for the selected fabric.
- Choose gross-plus-loss or net-coverage arithmetic consistently.
- Round rolls and compare usable widths and lengths with the layout.
Planning boundary
This estimates material coverage and does not specify drainage, erosion control or the suitability of landscape fabric.
Sources checked
Can the printed roll area be used unchanged?
Only when the rest of your calculation separately accounts for the actual seam and cutting requirements.
Does the result include fixing pins?
No. Prepare a separate fixing quantity using the chosen layout and product instructions.