Skip to content
ENExplore Calculators

Soil Bearing Capacity Calculator

Work out soil bearing capacity instantly with clear inputs, formula shown and shareable results.

About Soil Bearing Capacity Calculator

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.

Formulas

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

Worked example

With the default values below, Soil Bearing Capacity Calculator returns Safe bearing capacity of 283.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Soil cohesionminimum 0 kPa
20 kPa
Angle of internal frictionaccepts 1–45 °
25 °
Footing widthminimum 0.1 m
1.5 m
Founding depthminimum 0.1 m
1.5 m

Results

Safe bearing capacity
283.0 kPa
Ultimate bearing capacity
849.1 kPa
Bearing capacity factor Nc
20.721
Bearing capacity factor Nq
10.662

Step by step

  1. 1Values used
  2. 2Ultimate capacity
  3. 3Factors
  4. 4Safe bearing capacity= 283.0 kPa
  5. 5Ultimate bearing capacity= 849.1 kPa
  6. 6Bearing capacity factor Nc= 20.721
  7. 7Bearing capacity factor Nq= 10.662

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Preliminary estimate only. Foundation design must be based on a site investigation and verified by a qualified geotechnical engineer.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Foundation design must be based on a site investigation and verified by a qualified geotechnical engineer.

Frequently Asked Questions

How is the Soil Bearing Capacity figure worked out?

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.

Why is the factor of safety so large?

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.

What values do I need to enter?

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.

Related Calculators

Soil Bearing Capacity Calculator | Calcrivo