Slope Stability Factor of Safety Calculator
Calculate slope factor of safety (FS) via the infinite slope method.
Enter angle, cohesion, friction angle, and groundwater depth.
FS above 1.5 is stable.
Factor of Safety
Infinite Slope Method FS = (c + (γ·z·cos²β − u) × tan φ) / (γ·z·sin β·cos β)
Where c = cohesion (kPa), γ = unit weight (kN/m³), z = depth to failure plane (m), β = slope angle (°), φ = friction angle (°), u = pore water pressure (kPa).
Pore Water Pressure For a dry slope: u = 0. For a fully saturated slope (water table at surface): u = γw × z (where γw = 9.81 kN/m³).
Interpretation FS < 1.0: Failure likely. FS 1.0–1.25: Marginally stable. FS 1.25–1.5: Adequate stability. FS > 1.5: Stable.