Retaining Wall Design Calculator

Calculate active earth pressure, overturning moment, and sliding forces on a retaining wall using Rankine's theory.

Inputs

Wall Height (H)

IBC: >4 ft requires engineering; highway walls per AASHTO LRFD; typical gravity walls 4–8 ft, cantilever 8–20 ft

Soil Unit Weight (γ)

pcf

Friction Angle (φ)

ASTM D3080: compacted sand 30–35°; gravel 35–42°; use 30° conservative for unknown backfill

Surcharge Load

psf

AASHTO: 250 psf highway live load; parking/storage 100–250 psf; no surcharge=0 psf

Tab to move between fields

Results

Total Active Force

2,000 lb/ft

Overturning Moment

6,667 ft·lb/ft

Active Pressure Coeff (Ka)0.33

Passive Pressure Coeff (Kp)3

Sliding Force2,000 lb/ft

Max Pressure at Base400 psf

How to Use This Calculator

Enter wall height (H), soil unit weight (γ), friction angle (φ), and surcharge load.
Review Active Pressure Coefficient (Ka), Passive Pressure Coefficient (Kp), Total Active Force, and Overturning Moment.
Check overturning and sliding factors of safety — minimum 2.0 for overturning, 1.5 for sliding.

How the result changes with Wall Height (H)

Wall Height (H)	Total Active Force	Overturning Moment
6.8	925 lb/ft	2,096 ft·lb/ft
19	7,220 lb/ft	45,727 ft·lb/ft
33	21,780 lb/ft	239,580 ft·lb/ft
45	40,500 lb/ft	607,500 ft·lb/ft

What each input means

Wall Height (H): Total height of the retaining wall from base to top. IBC and most jurisdictions require engineered design for walls over 4 ft; AASHTO LRFD for highway walls. Check local building codes for permit thresholds.
Soil Unit Weight (γ): Unit weight of the retained soil. Typical granular fill is 110-130 pcf.
Friction Angle (φ): Internal friction angle of the backfill soil per ASTM D3080. Compacted clean sand ≈ 30–35°; compacted gravel ≈ 35–42°; mixed fill ≈ 28–32°. Use 30° for conservative design when testing is unavailable.
Surcharge Load: Uniform surcharge pressure on the soil surface behind the wall from traffic, storage, or adjacent structures. AASHTO recommends 250 psf for highway live load surcharge; ASCE 7 specifies equivalent fluid pressure method for restrained walls.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Wall Height (H) = 10, Soil Unit Weight (γ) = 120, Friction Angle (φ) = 30, Surcharge Load = 0 = 4 input(s) provided
Calculate Total Active Force
Total Active Force
2000 = 2000
Calculate Overturning Moment
Overturning Moment
6667 = 6667
Calculate Active Pressure Coeff
Active Pressure Coeff = Ka
0.3333 = 0.3333
Calculate Passive Pressure Coeff
Passive Pressure Coeff = Kp
3 = 3

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