About this tool Calculate the soil infiltration rate from simple field test data. Enter the volume of water infiltrated, the test area, and the duration to get the infiltration rate in mm/hr and equivalent hydraulic conductivity in m/s.
Results are classified from Very High (gravel) to Very Low (intact clay) following BS EN ISO 14688-2 permeability ranges. Useful for soakaway feasibility, drainage design, and preliminary site assessment.
Works with any simple infiltration test — ring infiltrometer, trial pit flooding, or constant head tests. For BRE 365 soakaway tests with falling head, use the dedicated BRE 365 Infiltration Calculator.
How to use this tool 1. Enter the volume infiltrated — total litres of water that soaked into the ground during the test.
2. Enter the test area — area of the infiltration ring or pit base in m².
3. Enter the test duration — in minutes. Read the rate and permeability class.
Technical information Rate = Volume / (Area × Time)
Permeability classes follow BS EN ISO 14688-2 and Terzaghi & Peck: Very High (>10⁻³ m/s) to Very Low (<10⁻⁹ m/s).
Limitations This calculates a bulk infiltration rate, not true hydraulic conductivity. The result is influenced by initial saturation, head of water, soil structure, and test method.
For soakaway design to BRE 365, use the dedicated BRE 365 calculator which accounts for falling head conditions and the specific test methodology.
Field infiltration rates can vary significantly over short distances. Always test at multiple locations and depths representative of the proposed infiltration level.
Revision history 14 July 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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