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The soil's cohesion.
Zero for purely granular (cohesionless) soils like clean sand.
The soil's angle of internal friction.
0° for purely cohesive soils (saturated clay, undrained); 28-40° is typical for sands and gravels.
The overburden pressure at the footing's base level.
Typically the soil unit weight multiplied by the footing's depth of embedment.
The soil's unit weight below the footing.
The bulk unit weight of the soil beneath the founding level, from a site investigation rather than a table where one exists. Below the water table use the SUBMERGED unit weight — bulk minus about 9.81 kN/m³ — because buoyancy removes roughly 40% of the term this contributes, and using the bulk figure there overstates capacity in exactly the condition where capacity matters most.
The footing's width.
For a strip footing this is the narrow dimension.
Ultimate bearing capacity
22,300 psf
This gives ULTIMATE bearing capacity — a real design divides this by a factor of safety (commonly 2.5-3.0) to get the allowable bearing pressure, and applies shape/depth/inclination correction factors for non-strip footings, which this simplified strip-footing calculator omits.
- Nc
- 30.14
- Nq
- 18.4
- Nγ
- 22.4
They open the calculator with your figures already in it
Shallow Foundation Bearing Capacity Calculator (Vesic Factors): 22,324 psf — 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)
- General bearing capacity equation: qu = c×Nc + q×Nq + 0.5×γ×B×Nγ, with the Prandtl–Reissner factors Nq = e^(π·tanφ)·tan²(45+φ/2) and Nc = (Nq−1)·cotφ (Nc = 5.14 at φ=0), and Vesic's Nγ = 2(Nq+1)·tanφ
- These are the factors Meyerhof, Hansen and Vesic use, not Terzaghi's own 1943 factors. Terzaghi's run higher — roughly 10–22% across this calculator's friction-angle range — so a capacity from this page is the more conservative of the two
Inputs used
- Soil Cohesion (c)
- 208.85 psf
- Friction Angle (φ, degrees)
- 30
- Overburden (Surcharge) Pressure (q)
- 417.71 psf
- Soil Unit Weight (γ)
- 114.59 pcf
- Footing Width (B)
- 6.5 ft
Intermediate steps
- Nc
- 30.14
- Nq
- 18.4
- Nγ
- 22.4
Confidence note: This gives ULTIMATE bearing capacity — a real design divides this by a factor of safety (commonly 2.5-3.0) to get the allowable bearing pressure, and applies shape/depth/inclination correction factors for non-strip footings, which this simplified strip-footing calculator omits.
What this calculation does not cover
- Ultimate capacity at shear failure, with no settlement check. On sand and on stiff clay the working pressure is usually set by total and differential settlement rather than by bearing failure, so a footing can clear this figure and still move more than the structure above it will tolerate.
- Groundwater is not in the model. There is no water table input, and when water stands at or above founding level both the surcharge term and the 0.5×γ×B×Nγ term have to be built from effective stresses — the unit weight field will not even accept a submerged unit weight, its floor being 14 kN/m³ (89 pcf). Reduce q and γ yourself before entering them, or the capacity reads high.
- Strip footings under a vertical, centrally applied load only. No shape, depth, load-inclination or ground/base-slope factors are applied, so a square or rectangular pad, a circular base, a raft or an eccentrically loaded footing falls outside it; eccentricity also calls for the effective-width reduction B − 2e, which this does not do.
- General shear failure is assumed at every friction angle. Loose sands and soft compressible clays fail by local or punching shear, where these factors overstate capacity, and no reduction to c or tanφ is made for it.
- One uniform soil, taken to extend through the whole failure wedge — roughly one to two footing widths below the base. Layering is invisible to it: a soft stratum under a firm crust, or fill over natural ground, returns the crust's capacity. This is a screening figure against parameters someone else measured, not a foundation design, and it does not replace a site investigation or an engineer's allowable bearing pressure.
Add the equipment this sizes
This result is a specification — 22,300 psf — 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 citations2
- General bearing capacity equation: qu = c×Nc + q×Nq + 0.5×γ×B×Nγ, with the Prandtl–Reissner factors Nq = e^(π·tanφ)·tan²(45+φ/2) and Nc = (Nq−1)·cotφ (Nc = 5.14 at φ=0), and Vesic's Nγ = 2(Nq+1)·tanφ
- These are the factors Meyerhof, Hansen and Vesic use, not Terzaghi's own 1943 factors. Terzaghi's run higher — roughly 10–22% across this calculator's friction-angle range — so a capacity from this page is the more conservative of the two
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