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Geotextile Riprap Fabric Overlap Calculator

Estimate the total geotextile filter fabric needed under a riprap slope, accounting for overlap between adjacent rolls.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax
49.21 ft65.62 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Fabric needed

3632.82 ft²

Check your inputs

Doesn't include extra fabric for anchor trenches at the slope crest/toe or for irregular slope shapes — add a margin for those if applicable.

Number of roll widths needed
5 rolls
Effective coverage width per roll
13.78 ft

With the figures above, the fabric needed comes to 338 m². Note that slope width sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. The method behind this is well established, though site conditions and material batches will move it somewhat. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Standard geotextile installation requires adjacent rolls to overlap by a minimum margin, reducing the effective coverage width per roll below its full manufactured width

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why does overlap reduce the effective coverage width?
Each roll's edge must overlap the next roll's edge to prevent gaps where soil can migrate through — that overlapped strip counts twice (once for each adjacent roll), so it doesn't add new net coverage width.
Does more overlap always mean better performance?
Up to a point — beyond the specified minimum, extra overlap mainly adds material cost without meaningfully improving performance, so match your project's actual specification rather than over-ordering.
Should seams be sewn or just overlapped?
For most riprap applications a simple shingled overlap in the direction of water flow is standard, but high-flow or critical erosion-control applications sometimes specify sewn or heat-bonded seams — check your project specification.