Southwest Environmental Limited

^{Environmental Consultancy Services to Industry, Business and Individuals} Email Us

02076 920 670

01392 927 961

01612 970 026

01173 270 092

Geotechnical Bearing Capacity Calculator

The below tool is provided for you to freely use, for non-official, don't blame us, it's your responsibility type purposes. For goodness sake please don't actually use it to build anything with. Scroll down for help filling out boxes.

Need Physical Site Data?

SWEL provides CBR Testing, Phase 2 Intrusive Site Investigations, and Soils Analysis across the UK. If you are a developer, structural engineer, or groundworks contractor finalizing foundation designs, we can supply the exact ground data you need. Ready to get started? Email Us for a Fast Quote or call our technical team on 02076 920 670.

Enter the parameters below to calculate the ultimate bearing capacity in kN/m².

SPT N Value (for reference):

Shear Strength / Cohesion (c' or cu in kPa):

Phi Angle ($\phi$) (degrees):

Footing Width (B in meters):

Footing Depth (Df in meters):

Soil Unit Weight ($\gamma$ in kN/m³):

Factor of Safety

The above figure will need to be divided by the correct factor of safety. 3 is used for most stuff. So divide it by 3 to get allowable bearing pressure. That's what most people use.

Help Filling Out Boxes

Below we have provided a series of reference values you can use to fill out the boxes; the more actual field data (from the actual soil) you can put in, the better.

Shear Strength

Very Soft (Less Than 20 kPa): Very easily deformed. It will feel like thick mud or toothpaste and will flow with slight pressure.
Soft (0 - 40 kPa): Easily deformed by finger pressure. It will feel yielding.
Firm (40 - 75 kPa): Deformed with noticeable effort. It will resist moderate pressure but will still change shape.
Stiff (75 - 150 kPa): Deformed with great difficulty. Requires significant effort to change its shape.
Very Stiff to Hard (Over 150 kPa): Cannot be easily deformed by hand pressure. It will feel like a hard lump.

Phi Angle Correlation (φ)

If you want you can put a zero "0" in the Phi Angle box for Clays. This will give you the weakest value. For gravels and sands, you can estimate Phi based on your SPT N-Value:

SPT N-Value	Relative Density	Approx. Phi Angle (φ)
0 - 4	Very Loose	< 28°
4 - 10	Loose	28° - 30°
10 - 30	Medium Dense	30° - 36°
30 - 50	Dense	36° - 41°
> 50	Very Dense	> 41°

Typical Soil Unit Weights (γ)

Soil Type	Typical Unit Weight (γ)
Peat	12 kN/m³
Soft Clay	16 - 18 kN/m³
Stiff Clay	18 - 20 kN/m³
Loose Sand/Gravel	17 - 19 kN/m³
Dense Sand/Gravel	20 - 22 kN/m³

Footing Dimensions

Type in dimensions of your footing directly into the calculator fields.

The below section was written by a machine.

Geotechnical Bearing Capacity Calculator for Foundation Design

This online Geotechnical Bearing Capacity Calculator is a technical tool designed to assist engineers and developers in estimating the load-bearing capabilities of shallow foundations. By inputting key soil parameters—such as cohesion, internal friction angle, and unit weight—users can perform rapid assessments based on established geotechnical principles.

While this tool provides a valuable initial estimate, accurate foundation design requires high-quality site data. We recommend pairing these calculations with professional Geotechnical Site Investigations to verify underground conditions.