About this tool Calculate the coefficient of variation (CoV) — the standard deviation expressed as a percentage of the mean. This is the standard measure of relative variability used in geotechnical engineering to assess data quality and ground heterogeneity.
Results are colour-coded (low/moderate/high/very high variability) and compared against published benchmark CoV values for common geotechnical properties — after Phoon & Kulhawy (1999). This tells you whether your dataset's variability is normal for the property being measured or unusually scattered.
Useful for checking lab data quality, comparing variability across sites, and informing the choice of characteristic values per Eurocode 7.
How to use this tool 1. Enter your data — paste values separated by commas, spaces, or new lines.
2. Check the CoV — compare against the benchmark table to see if your variability is typical for the property you're measuring.
3. Interpret the colour coding — green < 10%, amber 10-25%, orange 25-50%, red > 50%.
Technical information CoV (%) = (s / |x̄|) × 100
Uses sample standard deviation (n-1). The benchmark table is based on Phoon & Kulhawy (1999) — the most widely cited source for geotechnical property variability in EC7-aligned practice.
Limitations CoV is only meaningful for ratio-scale data with a non-zero mean. It is not appropriate for properties that can take negative values (e.g. temperature in °C) or for data centred near zero.
Benchmark CoV ranges are indicative. Actual variability depends on site geology, sampling quality, lab testing procedures, and spatial extent of the dataset.
High CoV does not necessarily mean poor data — it may reflect genuine ground heterogeneity. Low CoV in a dataset with few samples may give false confidence. Always consider sample size alongside CoV.
Revision history 5 May 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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