Retaining Wall Calculator
Will a gravity retaining wall stay put? Checks the three ways it fails — overturning, sliding and bearing — with safety factors and a clear pass or review verdict.
Three Ways a Retaining Wall Fails
A retaining wall holds back soil that is constantly trying to push it over, shove it forward, or sink it into the ground. Stability comes down to three checks, and a wall has to pass all three:
| Failure mode | What resists it | Typical safety factor |
|---|---|---|
| Overturning | Wall weight about the toe | 2.0 |
| Sliding | Friction under the base | 1.5 |
| Bearing | Soil capacity under the toe | peak below allowable |
The Push: Active Earth Pressure
The soil behind the wall pushes with a force that grows with the square of the height. Using Rankine theory for a level granular backfill, the active pressure coefficient is:
A higher friction angle φ means a lower Ka and less push. The total thrust acts at one third of the height up from the base, which is what drives the overturning moment.
Water Is the Real Enemy
Most retaining walls that fail do so because water built up behind them, adding hydrostatic pressure the wall was never sized for. This calculator assumes a drained backfill — so the single most important thing you can build into a real wall is drainage: weep holes, a gravel zone and a drain pipe.
Frequently Asked Questions
What is the middle-third rule?
If the resultant force stays within the middle third of the base, the whole base stays in compression. Outside it, the heel lifts into tension and bearing concentrates at the toe. The calculator flags this even when the other checks pass.
Gravity or cantilever wall?
This tool models a gravity wall, which resists by sheer mass. Cantilever walls add a reinforced stem and use the weight of soil on the heel – a related but separate calculation.
What friction angle should I use?
Clean sand and gravel are around 30 to 36 degrees; silty or clayey soils are lower. Use the value from your soil report; guessing high is unconservative.
Related calculators
- Soil Bearing Capacity Calculator — the allowable pressure this wall must stay under.
- Concrete Volume Calculator — concrete for the wall and base.
- Block Wall Calculator — for masonry retaining walls.
- Footing Size Calculator — size the base footing.