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The height of soil being retained.
From the top of the retained soil down to the base of the stem, which is usually the top of the footing rather than finished ground level in front of the wall. The pressure resultant goes with the SQUARE of this height, so a wall entered 10% short is about 19% light on load — this is the single most sensitive number on the page, and it is worth taking from a section rather than from a plan.
The soil's angle of internal friction.
From a shear test if one exists. Where it does not, a drained sand is commonly taken somewhere in the low-to-mid thirties and a compacted granular backfill higher, but the number matters: the active coefficient falls quickly as φ rises, so two degrees of optimism is several per cent off the load. Clay retained behind a wall is a different problem — undrained clay does not behave as this Rankine arrangement assumes, and its long-term drained strength is the one that governs.
The retained soil's unit weight.
The unit weight of the backfill behind the wall, not of the ground it stands on. Compacted granular fill is heavier than the loose material delivered, and a saturated backfill is heavier again — which is why drainage behind a wall is a structural measure and not a landscaping one. If the backfill can saturate, this calculation understates the case regardless of the number entered, because water adds its own pressure that no soil unit weight captures.
Any uniform load applied at ground level behind the wall.
E.g. a parking area, driveway, or equipment laydown area above the retained soil.
Active pressure resultant
2,610 lbf/ft
Assumes a uniform surcharge covering the full retained soil surface — a surcharge limited to only part of the backfill (e.g. a small equipment pad) distributes differently and needs a more detailed analysis.
- Rankine active coefficient (Ka)
- 0.33
- Soil weight component
- 1,909.76 lbf/ft
- Surcharge component
- 696.18 lbf/ft
They open the calculator with your figures already in it
Rankine Active Earth Pressure with Surcharge Calculator: 2,606 lbf/ft — 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 with a uniform surcharge: Pa = 0.5 x Ka x γ x H² + q x Ka x H, where q is the uniform surcharge pressure applied at the ground surface behind the wall
Inputs used
- Wall Height (Retained Soil)
- 10 ft
- Soil Friction Angle (φ, degrees)
- 30
- Soil Unit Weight (γ)
- 114.59 pcf
- Uniform Surcharge Load (q)
- 208.85 psf
Intermediate steps
- Rankine active coefficient (Ka)
- 0.33
- Soil weight component
- 1,909.76 lbf/ft
- Surcharge component
- 696.18 lbf/ft
Confidence note: Assumes a uniform surcharge covering the full retained soil surface — a surcharge limited to only part of the backfill (e.g. a small equipment pad) distributes differently and needs a more detailed analysis.
What this calculation does not cover
- There is no water in this model. Below a water table the retained soil pushes with its buoyant weight while the water adds its own full hydrostatic pressure, which Ka does not reduce, so a wall with a blocked, silted or missing drain carries substantially more than the figure here. Perched water on a clay horizon and seepage after rain are not checked at all.
- Ka is the level-ground Rankine coefficient for cohesionless soil against a vertical, frictionless wall. It carries no term for a sloping backfill, cohesion, wall friction or a layered fill, and a backslope raises the coefficient itself rather than just the load, so entering a slope through the surcharge field does not reproduce it.
- Active pressure only develops if the wall moves enough for the soil behind it to relax. A basement wall, a propped or tied-back wall, or one keyed into rock attracts at-rest pressure, which is higher than this; so does fill compacted hard against the back of the wall, where plant locks in pressure above the active value near the top.
- No seismic loading and no factor of safety. This is an unfactored static resultant, and a Mononobe-Okabe or equivalent analysis is a separate check wherever seismic design applies.
- This is a load, not a design. It does not check sliding, overturning, bearing capacity or global slope stability, does not size the wall, its base or any reinforcement, and it gives the magnitude of each component without the height it acts at — the soil and surcharge resultants sit at different points, and you need both before any stability check can be run.
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This result is a specification — 2,610 lbf/ft — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
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 citations1
- Rankine active earth pressure with a uniform surcharge: Pa = 0.5 x Ka x γ x H² + q x Ka x H, where q is the uniform surcharge pressure applied at the ground surface behind the wall
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