Retaining Wall Earth Pressure Calculator

It is the ratio of horizontal to vertical stress in soil that is free to move slightly away from the wall. For level granular backfill it depends on the soil friction angle. For a typical granular soil with a 30 degree friction angle, Ka works out to 0.333, so about a third of the soil's weight pushes horizontally.

Because the pressure grows with depth in a triangular distribution, the resultant force acts at one third of the wall height above the base.

No. It is a simplified Rankine estimate for level backfill with no surcharge or water. It is a planning estimate only, so consult a licensed engineer before building.

As a rough guide: loose dry sand runs about 95 to 105 pcf, dense sand 110 to 130 pcf, well compacted gravel 120 to 140 pcf, and clay 100 to 120 pcf. Without a geotechnical report, 120 pcf is a conservative value for granular backfill.

No. This calculator assumes drained backfill with no hydrostatic pressure. If water is trapped behind the wall, the pressure rises sharply because the weight of the water adds to the soil thrust. Always install French drains or perforated pipe to relieve water from the backfill.

Almost always. Most codes require an engineer-signed design for walls taller than 4 feet of exposed height. This tool is useful for an early idea, but it does not replace the professional analysis that accounts for surcharges, seismic loads, water, cohesion, and the real geometry of the site.