Retaining Wall Overturning Safety Factor Calculator
This calculator checks the overturning stability of a simple gravity or cantilever retaining wall. The factor of safety against overturning (FSo) is the ratio of the stabilising (resisting) moment about the wall toe to the destabilising (overturning) moment. The overturning moment is generated by the active earth pressure resultant acting on the retained height. The resisting moment comes from the weight of the wall and the soil above its heel. This simplified model assumes Rankine active pressure with a horizontal retained surface, no surcharge, and a vertical wall face. A minimum FSo of 1.5 is generally required.
Overturning stability formulas
Ka = tan²(45 - phi/2)
Pa = 0.5 × Ka × gamma × H²
Mo = Pa × H/3
Mr = Wr × xr
FSo = Mr / Mo
Pa acts at H/3 above the base for a triangular pressure distribution. FSo must be at least 1.5 (non-seismic) per common practice. Units: consistent foot and kip or metre and kN.
Additional stability checks required
- Sliding stability: FS(sliding) = (Wr * tan(delta)) / Pa, where delta is the wall-base friction angle. Minimum FS = 1.5.
- Bearing capacity: the resultant of all forces must fall within the middle third of the base to prevent tension at the heel and ensure adequate bearing.
- Settlement: check the maximum bearing pressure against the allowable soil bearing capacity from a geotechnical report.
- Global stability: deep-seated slip circle analysis may be required for walls on soft or sloping ground.
Frequently asked questions
What is the overturning safety factor for a retaining wall?
The factor of safety against overturning (FSo) equals the sum of moments resisting overturning divided by the sum of moments causing overturning, both taken about the toe of the wall. A minimum FSo of 1.5 is typically required by codes for non-seismic conditions; 2.0 is common for critical structures.
What causes overturning in a retaining wall?
Overturning is driven primarily by the horizontal component of active earth pressure, which acts on the retained face of the wall. Surcharge loads and water pressure can add to this overturning moment. The moment arm is the height to the resultant force application point.
What resists overturning?
Resisting moments come from: the self-weight of the wall (stem and footing), the weight of soil above the footing heel, and the vertical component of inclined earth pressure. All weights act at their respective moment arms measured from the toe.
What is the Rankine active earth pressure coefficient Ka?
For a vertical wall with horizontal backfill, Ka = tan^2(45 - phi/2), where phi is the soil friction angle. For a typical sandy soil with phi = 30 degrees, Ka = 0.333. For a cohesive backfill, additional terms apply.
Does this calculator account for seismic loading?
No. Seismic design of retaining walls uses the Mononobe-Okabe method to compute an increased active pressure coefficient. For seismic conditions, refer to ASCE 7 Chapter 11 and AASHTO LRFD Bridge Design Specifications.
Official sources
- American Concrete Institute: ACI 318 Building Code Requirements for Structural Concrete.
- American Society of Civil Engineers: ASCE 7 Minimum Design Loads for Buildings and Other Structures.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.