Soil Bearing Capacity Calculator

Estimate ultimate and allowable bearing capacity for a shallow footing from soil shear strength parameters (c, φ), unit weight, and footing geometry, using the general bearing capacity equation with Vesic factors and De Beer shape factors.

Educational / preliminary estimating tool. Results use published correlations and idealized assumptions (homogeneous soil, no groundwater effects unless stated). They are not a substitute for a site-specific investigation and design by a licensed geotechnical engineer.

Soil & Footing Parameters

Cohesion c

psf

Friction Angle φ

Soil Unit Weight γ

pcf

Footing Depth D_f

Footing Width B

Footing Shape

Factor of Safety

Enter soil parameters and footing geometry to estimate bearing capacity.

The equation

q_u = c·N_c·s_c + γ·D_f·N_q·s_q + 0.5·γ·B·N_γ·s_γ

The three terms capture cohesion, surcharge from embedment, and soil self-weight below the footing. N_q = e^π·tanφ·tan²(45+φ/2), N_c = (N_q−1)·cotφ, and N_γ = 2(N_q+1)·tanφ (Vesic). Shape factors follow De Beer: strip footings use B/L = 0, square and circular use B/L = 1. Allowable capacity divides ultimate by your factor of safety — 3 is the conventional default for shallow foundations.

Assumptions and limits

This is the general-shear solution for a homogeneous soil with the groundwater table well below the influence zone (deeper than about B below the footing). A shallow water table can cut the N_γ term roughly in half; layered profiles, inclined loads, and local/punching shear in loose soils all require the extended corrections in a geotechnical design. Use undrained parameters (φ = 0, c = s_u) for short-term clay capacity and drained parameters for sands and long-term behavior.

Frequently Asked Questions

What is a typical allowable bearing capacity?

Common presumptive values run from about 1,500 psf (72 kPa) for soft clay to 3,000–4,000 psf for stiff clay or medium-dense sand, and much higher on dense gravel or rock. Site-specific calculation beats presumptive tables.

What factor of safety is used for bearing capacity?

3 is the long-standing convention for shallow foundations under service loads, reflecting the consequences of a bearing failure and uncertainty in soil parameters.

Does groundwater reduce bearing capacity?

Yes — buoyancy reduces the effective unit weight in the surcharge and self-weight terms. A water table at footing level can reduce capacity by roughly a third to a half versus a dry profile.