ToolsIn-Situ Testing ToolsSPT Analysis

SPT Energy Correction Calculator

Apply comprehensive SPT corrections including energy, borehole diameter, sampler type and rod length corrections.

Last updated 11 February 2026

About this tool

Calculate fully corrected SPT N₆₀ values with comprehensive energy, equipment and procedural corrections following ASTM D1586 and international standards.

This calculator applies multiple correction factors (CE, CB, CS, CR) to normalize SPT results for consistent comparison across different equipment, drilling conditions, and testing procedures.

How to use this tool

Enter measured N-value. Input the raw blow count from field testing.
Select hammer type. Choose the hammer used (sets the energy ratio).
Enter rod length. Input the drill rod length at test depth (meters).
Select borehole diameter. Choose from standard borehole sizes (mm).
Select sampler type. Specify whether sampler has liner, no liner, or is standard.

Correction factors

CE (Energy): Normalizes hammer energy to 60% reference. Values vary by hammer type: Donut (~45%), Safety (~60%), Automatic (~78%).

CB (Borehole): Corrects for borehole diameter. Larger holes (150-200mm) increase measured N-values.

CS (Sampler): Accounts for sampler configuration. Liners increase internal friction, inflating the measured blow count. The correction factor (0.8) compensates for this.

CR (Rod Length): Corrects for energy loss in short rods. Significant below 10m depth.

Limitations

Correction factors are based on typical equipment and may vary with specific manufacturers.
Energy ratios should ideally be measured on site for critical projects.
This calculator does not include overburden correction (CN) - use the SPT N-value Calculator for that.

Technical information

Formula: N₆₀ = N_measured × CE × CB × CS × CR

CE: Energy Ratio (ER) / 60

CB: 1.0 (65-115mm), 1.05 (150mm), 1.15 (200mm)

CS: 0.8 (with liner), 1.0 (standard, without liner)

CR: 0.75 (<3m), 0.8 (3-4m), 0.85 (4-6m), 0.95 (6-10m), 1.0 (≥10m)

Revision history

11 February 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.

Measured N-value

Hammer type

Rod length (meters)

Borehole diameter

Sampler type