Retaining wall pressure calculator
Wall height, soil unit weight, friction angle and surcharge: you get Ka, soil and surcharge thrust, the resultant height and the overturning moment.
Total active thrust
18.67 kN/m
- Active pressure coefficient Ka0.33
- Soil thrust12 kN/m
- Surcharge thrust6.67 kN/m
- Resultant height above base2.592 ft
- Overturning moment at base14.67 kN·m/m
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How it's calculated (visible formula)
Ka = tan²(45° − φ/2); Pa = ½·Ka·γ·H² + Ka·q·H; M = ½·Ka·γ·H²·H/3 + Ka·q·H·H/2
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Set the total retained soil height.
- Take soil unit weight and friction angle (ideally from a soils report).
- Compute Ka = tan²(45° − φ/2).
- Compute the triangular soil thrust and rectangular surcharge thrust.
- Get the resultant, its height and the overturning moment to check the wall.
Typical soil parameters
| Soil | γ (kN/m³) | φ |
|---|---|---|
| Loose sand | 17 | 30° |
| Dense sand | 19 | 35° |
| Gravel | 19 | 38° |
| Stiff clay | 19 | 22° |
Worked example: 6.5 ft (2 m) wall, γ = 18 kN/m³, φ = 30°, q = 10 kN/m²
- Ka = tan²(30°) = 0.333
- Soil: ½ × 0.333 × 18 × 2² = 12 kN/m
- Surcharge: 0.333 × 10 × 2 = 6.67 kN/m
→ Pa = 18.67 kN/m (≈1,280 lb/ft); base moment ≈ 14.7 kN·m/m.
Common mistakes
- Ignoring water: hydrostatic pressure can double the load.
- Using Rankine with a sloped backfill or battered wall face.
- Confusing active pressure with at-rest pressure (rigid or basement walls).
Pro tips
- Use the real surcharge: vehicles, stockpiles or a nearby footing.
- Without guaranteed drainage, add water pressure — it can double the load.
- For rigid or basement walls use at-rest K0 ≈ 1 − sin φ, which is larger than Ka.
- Check overturning and sliding with factors of safety (typically ≥ 1.5).
From calculation to quote
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FAQs
- What is Ka?
- The active earth pressure coefficient: the share of vertical soil pressure passed to a wall that yields slightly.
- What friction angle should I use?
- Sands 30–35°, gravels 35–40°, clays 20–25°. Use your geotechnical report when you have one.
- Can I design the wall with this?
- It's a preliminary check; overturning, sliding and bearing checks are done by an engineer.
- What surcharge for a parking area?
- Roughly 250 psf (12 kPa) for light vehicles is a common assumption; follow your local code.
- What is at-rest pressure?
- Pressure on a wall that can't move; higher than active pressure.
- Where does the resultant act?
- At H/3 above the base for soil and H/2 for uniform surcharge.
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.