Work out soil bearing capacity instantly with clear inputs, formula shown and shareable results.
Terzaghi's bearing capacity equation adds three contributions: cohesion, surcharge from the soil above founding level, and the self weight of the shear wedge beneath the footing. The bearing capacity factors follow from the friction angle, and a factor of safety of three on ultimate capacity gives the allowable pressure used in design.
Ultimate capacity
qu = c Nc + gamma D Nq + 0.5 gamma B Ngamma
Factors
Nq = e^(pi tan phi) tan²(45 + phi/2); Nc = (Nq - 1)/tan phi; Ngamma = 2(Nq + 1) tan phi
Preliminary estimate only. Foundation design must be based on a site investigation and verified by a qualified geotechnical engineer.
qu = c Nc + gamma D Nq + 0.5 gamma B Ngamma. Terzaghi's bearing capacity equation adds three contributions: cohesion, surcharge from the soil above founding level, and the self weight of the shear wedge beneath the footing.
It covers uncertainty in soil parameters, which vary widely across a site, and it also keeps settlement small. On many soils settlement rather than bearing failure governs the allowable pressure.
This calculator takes 4 inputs: Soil cohesion, Angle of internal friction, Footing width, Founding depth. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.