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Infinite Slope Stability Factor of Safety Calculator

Estimate the factor of safety against sliding for a long, uniform, cohesionless (dry) slope.

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

Factor of safety

1.72 (FS)

High confidence

Meets a common minimum target of FS ≥ 1.5 for long-term slope stability.

At the values currently entered, the factor of safety works out to 1.72 (FS). Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

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

  • Infinite slope stability, dry cohesionless soil: FS = tan(φ) / tan(β), where φ is the soil's friction angle and β is the slope angle — the classic simplified case where slope length is much greater than the failure depth

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Frequently asked questions

What does 'infinite slope' mean here?
It's an idealized model assuming the slope is long and uniform compared to the depth of the potential failure surface — a reasonable approximation for shallow slides on natural or constructed slopes, but not for deep-seated rotational failures.
Why does this only apply to dry, cohesionless soil?
Adding cohesion or accounting for seepage/saturation (a major real-world factor in most slope failures) requires additional terms in the stability equation — this simplified version isolates the pure friction-based case for quick screening.
What if groundwater seepage is present?
Seepage parallel to the slope significantly reduces the factor of safety (often roughly by half for a fully saturated slope) compared to the dry case — always account for seepage conditions in a full design-level slope stability analysis.