Geology Skewness Folk Ward Calculator
Folk–Ward normalized central and tail PHI asymmetry, not moment skew. Caller independently establishes matching units, evidence, method edition and applicability; output is not compliance, diagnosis, work-safety approval, geological identity or validated hazard prediction.
Description
Graphic skewness describes asymmetry around the median of a grain-size distribution.
Graphic skewness describes asymmetry around the median of a grain-size distribution.1
The Folk–Ward expression uses both central and tail percentile relationships and requires nonzero denominator spreads. Use this tool to calculate skewness folk ward from the supplied measurements and assumptions.
When to use Geology Skewness Folk Ward Calculator
Use this tool to calculate skewness folk ward from the supplied measurements and assumptions. Establish the measurement units, sampled interval, calibration or model edition and geological assumptions before entering data.
How to use Geology Skewness Folk Ward Calculator and understand its results
- Establish the measurement units, sampled interval, calibration or model edition and geological assumptions before entering data.
- Enter phi5, phi16, phi50, phi84, phi95, using the field meanings and rules below, then run the tool.
- Read graphicSkewness. Interpret the fields using their units, signs and evidence conventions below.
- If input validation fails, correct the reported field and run again. Before applying the result, check reference scope, model assumptions and any missing evidence or placeholder values.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| phi5 | Phi5 | number | Required |
| phi16 | Phi16 | number | Required |
| phi50 | Phi50 | number | Required |
| phi84 | Phi84 | number | Required |
| phi95 | Phi95 | number | Required |
Supply finite nondecreasing phi5, phi16, phi50, phi84 and phi95. Require phi84>phi16 and phi95>phi5 so both normalized terms are defined. Add the median-centered central and tail asymmetry terms; no skewness category is installed.
skewness=(phi16+phi84−2phi50)/[2(phi84−phi16)]+(phi5+phi95−2phi50)/[2(phi95−phi5)] Use the exact units, boundary rules, ordering and missing-evidence conventions above.
| Output field | Meaning | Value type |
|---|---|---|
| graphicSkewness | Graphic Skewness; follow the units, sign, ordering and evidence convention stated above | number |
{
"input": {
"phi5": -2,
"phi16": -1,
"phi50": 0,
"phi84": 2,
"phi95": 4
},
"output": {
"graphicSkewness": 0.3333333333333333
}
}Limitations and assumptions
The Folk–Ward expression uses both central and tail percentile relationships and requires nonzero denominator spreads. Interpretation depends on the units, sampling scope and exact model described above.
All listed fields require explicit values. Unexpected fields, incorrect types, nonfinite numbers and sparse evidence arrays fail validation; the specific bounds and alignment requirements are stated above. Extremely large inputs or outputs can also be rejected. An input error is distinct from a successful result reporting false, no matches or missing evidence.
Alternative or Complementary methods
Use Geology Wentworth Phi To Mm Calculator for this related task: The phi grain-size scale is logarithmic, with increasing phi corresponding to decreasing diameter.
Use Geology Wentworth Grain Size Phi Calculator when its separate inputs and assumptions fit the question: A phi value is the negative base-two logarithm of grain diameter measured in millimeters.
References
-
Geology Skewness Folk Ward Calculator — tool.io
Similar or alternative tools
- Geology Wentworth Phi To Mm Calculator
The phi grain-size scale is logarithmic, with increasing phi corresponding to decreasing diameter.
- Geology Wentworth Grain Size Phi Calculator
A phi value is the negative base-two logarithm of grain diameter measured in millimeters.