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SPT Young's Modulus Calculator

Estimate Young's modulus (E) from corrected SPT N60 values using Bowles (1997) empirical correlations for sands, silts, and clays.

Last updated 23 March 2026

About this tool

Estimate the Young's modulus (E) of soil from corrected Standard Penetration Test (SPT) N60 values using the Bowles (1997) empirical correlations.

The tool applies soil-type-specific correlation factors to provide indicative stiffness values for preliminary settlement analysis and geotechnical design.

Young's modulus is a fundamental parameter for estimating soil deformation under load, used in foundation design, finite element modelling, and settlement calculations.

How to use this tool

Enter corrected N60 - input the SPT N60 value from field testing or your energy correction calculator.
Select soil type - choose the predominant material. The correlation factor is automatically determined by soil type.
Review the result - the tool outputs the estimated Young's modulus in both MPa and kPa, along with the applied correlation factor.

What is Young's modulus?

Young's modulus (E) is a measure of soil stiffness - it describes how much a soil will deform under an applied stress. Higher values indicate stiffer, less compressible soils.

In geotechnical engineering, E is used for:

Settlement estimation for shallow foundations
Subgrade reaction modulus calculations
Finite element and numerical modelling
Soil-structure interaction analysis

Technical information

The tool uses correlations from Bowles (1997) Table 5-6:

E = a x (N60 + b) (kPa)

Where a and b depend on soil type:

Clean sand (NC): E = 500 x (N60 + 15)
Clean sand (OC): E = 750 x (N60 + 15)
Silty sand / Silt: E = 300 x (N60 + 6)
Clayey sand: E = 320 x (N60 + 15)
Sandy silt: E = 300 x (N60 + 6)
Soft clay (saturated): E = 250 x (N60 + 15)

Reference: Bowles, J.E. (1997). Foundation Analysis and Design, 5th Edition, McGraw-Hill, Table 5-6.

Limitations

Correlations are empirical and provide indicative values only - site-specific lab testing (e.g. triaxial or oedometer) should govern final design.
Young's modulus is stress- and strain-dependent - SPT correlations give a single representative value, not a stress-strain curve.
Energy and overburden corrections must be applied before using N60.
Not suitable for stiff clays, soft rocks, or cemented soils where SPT-modulus correlations are unreliable.

Revision history

23 March 2026: Initial release.

Disclaimer

This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.

Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.

All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.

By using this tool, you accept full responsibility for how you interpret and apply the information provided.

Spotted an error? Let us know.

Corrected N-value (N₆₀)

Soil type