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The height of soil being retained, measured from the base of the wall.
This is the full height the active earth pressure acts against, not just the visible exposed face.
The soil's angle of internal friction — get this from a geotechnical report if available.
30° is a commonly assumed value for well-drained granular backfill; softer clay soils can be significantly lower (15-25°), which increases pressure on the wall.
The soil's unit weight (density x gravity).
18 kN/m³ is a commonly cited average for moist granular soil; check a geotechnical report for your specific site if one is available.
The weight of the wall itself (and any soil locked above its heel), per linear meter of wall.
Estimate from your block/material's published weight and wall geometry, or from a manufacturer's engineering table for segmental retaining wall units.
The width of the wall's footprint at its base.
A wider base generally improves both sliding and overturning resistance.
The friction coefficient between the wall's base and the soil beneath it.
0.5 is a commonly assumed value for concrete or masonry on compacted granular soil.
Governing safety factor
1.68 (safety factor)
The governing safety factor is 1.68, at or above the 1.5 these checks are commonly taken against. This is a simplified preliminary calculation on the assumptions entered, not a design. Being under the allowable pressure is not the whole ground question: settlement, groundwater and the footings alongside are all untouched here.
- Rankine active pressure coefficient (Ka)
- 0.33
- Active pressure resultant
- 305.56 lbf/ft
- Sliding safety factor
- 1.68
- Overturning safety factor
- 2.52
They open the calculator with your figures already in it
Retaining Wall Preliminary Stability Check: 1.68 (safety factor) — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Rankine active earth pressure coefficient: Ka = tan²(45° - φ/2), where φ is the soil's angle of internal friction
- Active earth pressure resultant: Pa = 0.5 x Ka x soil unit weight x height², acting at height/3 above the base
- Standard preliminary safety factor threshold for both sliding and overturning checks is 1.5, per common geotechnical practice
Inputs used
- Wall Height (Retained Soil)
- 4 ft
- Soil Friction Angle (φ, degrees)
- 30
- Soil Unit Weight
- 114.59 pcf
- Wall Self-Weight (kN per linear meter)
- 15
- Wall Base Width
- 2 ft
- Base Friction Coefficient
- 0.5
Intermediate steps
- Rankine active pressure coefficient (Ka)
- 0.33
- Active pressure resultant
- 305.56 lbf/ft
- Sliding safety factor
- 1.68
- Overturning safety factor
- 2.52
Confidence note: The governing safety factor is 1.68, at or above the 1.5 these checks are commonly taken against. This is a simplified preliminary calculation on the assumptions entered, not a design. Being under the allowable pressure is not the whole ground question: settlement, groundwater and the footings alongside are all untouched here.
What this calculation does not cover
- Bearing capacity of the soil beneath the footing is not checked — a wall can pass sliding and overturning and still settle or rotate.
- Assumes fully drained backfill. Hydrostatic pressure from saturated soil is an additional load not modelled here, and is a leading cause of real-world wall failure.
- No seismic loading. In seismic design categories this omission is significant and a Mononobe-Okabe (or equivalent) analysis is required.
- No surcharge from vehicles, structures or slopes above the wall.
- Global/deep-seated slope stability is not assessed.
Part of a bigger job
Or plan the space itself: measure it once, doors and windows included, and this figure comes back worked out on that space, with what goes with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations3
- Rankine active earth pressure coefficient: Ka = tan²(45° - φ/2), where φ is the soil's angle of internal friction
- Active earth pressure resultant: Pa = 0.5 x Ka x soil unit weight x height², acting at height/3 above the base
- Standard preliminary safety factor threshold for both sliding and overturning checks is 1.5, per common geotechnical practice
Cite this page
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.
Water pressure is not in this calculation at all, and a wall inside the margin on paper still comes apart early if the backfill and the drain are not built. Budget for the compacted granular backfill and the drain whatever the factor says.