About this tool Convert dynamic probe blow counts to equivalent SPT N60 values. Five probe types are supported: DPL (Light), DPM (Medium), DPH (Heavy), DPSH-A, and DPSH-B per EN ISO 22476-2. Each has a specific hammer mass, fall height, cone area, and SPT conversion factor.
DPSH-A and DPSH-B have the same hammer energy as the SPT (63.5 kg × 750mm), so the conversion is approximately 1:1. Lighter probes need a multiplication factor. Optional torque reading input corrects for rod friction.
Results include equivalent SPT N60 and granular soil density classification (very loose to very dense). Pairs with existing SPT tools for cross-referencing.
How to use this tool 1. Select probe type — DPL, DPM, DPH, DPSH-A, or DPSH-B.
2. Enter blow count — blows per 100mm (DPL/DPM/DPH) or per 300mm (DPSH).
3. Enter torque (optional) — for rod friction correction. High torque relative to blow count flags unreliable results.
Technical information Equivalent SPT N60 = N_dp × conversion factor
Conversion factors: DPL ×1.0, DPM ×1.5, DPH ×1.5, DPSH-A ×1.0, DPSH-B ×1.0. Based on energy ratio comparison per EN ISO 22476-2.
Limitations Conversion factors are approximate and soil-type dependent. Site-specific calibration against SPT results is recommended, especially for DPL, DPM, and DPH.
Dynamic probes do not recover samples. Soil type must be inferred from adjacent boreholes or trial pits.
Torque readings should be taken every metre per EN ISO 22476-2. If torque exceeds approximately 50% of the equivalent blow energy, results are unreliable below that depth.
Revision history 29 September 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.
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