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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.

The Geotechnical Bearing Capacity Calculator

Enter the SPT N Value (for reference/correlation), Shear Strength (Cohesion), Phi Angle, Footing Width, Footing Depth, and Soil Unit Weight to calculate the ultimate bearing capacity in kN/m². Note: This calculator uses a general Terzaghi's bearing capacity formula. Adjustments may be needed based on your specific sheet's correlations for factors and SPT N.

 

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 nearing 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 ( < 20 kPa / < 0.25 tsf): Very easily deformed. It will feel like thick mud or toothpaste and will flow with slight pressure.
  • Soft ( = 20 - 40 kPa / 0.25 - 0.5 tsf): Easily deformed by finger pressure. It will feel yielding.
  • Firm ( = 40 - 75 kPa / 0.5 - 1.0 tsf): Deformed with noticeable effort. It will resist moderate pressure but will still change shape.
  • Stiff ( = 75 - 150 kPa / 1.0 - 2.0 tsf): Deformed with great difficulty. Requires significant effort to change its shape.
  • Very Stiff to Hard ( > 150 kPa / > 2.0 tsf): Cannot be easily deformed by hand pressure. It will feel like a hard lump.

    • Phi Angle

    If you want you can put a zero "0" in the Phi Angle box. Put zero in for Clays. This will give you the weakest value, at end of calculation. But if you have an N Value (From an SPT Test) then you can use that to estimate Phi.

    For gravels and sands and such you can use:

    phi_angle_N_value_corelation

    Footing Dimensions

     Type in dimensions of your footing here.

    Soil Weight

    soildesnitys_by_type_KNM3

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    Help Filling Out Boxes

    Hopefully you will find this handy. Please don't use it for anything important.

    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. For projects in high-demand urban areas, our team provides rapid deployment across major hubs including London, Bristol, Manchester, Birmingham, and Leeds.

    Key Features of the Calculator

    National Technical Consultancy

    Foundation design is a critical pillar of structural integrity. Our experts operate nationally, providing detailed reports in cities such as Exeter, Plymouth, Sheffield, Newcastle, Nottingham, and Southampton. We also extend our geotechnical services into Scotland and Wales, covering Edinburgh, Glasgow, and Cardiff.

    For complex sites, bearing capacity analysis is often integrated with other environmental requirements. If your development includes new hardstanding, you may require a Sustainable Drainage Systems (SuDS) Strategy. Furthermore, we can assist with CBR Testing for road and pavement design or investigations for building near trees to mitigate subsidence risks.

    Professional Guidance for Your Project

    Beyond the calculator, Southwest Environmental Limited offers the professional authority (FGS/IES) required to sign off on formal geotechnical reports for planning and building control. If you are at the early stages of a project, consider our Zero Cost ESG Consultation to see how geotechnical stability fits into your broader sustainability strategy.

    With 15 years of industry experience and over 900 projects delivered, our team ensures your foundations are designed on solid ground, meeting both technical standards and regulatory expectations across the UK.