Grain Size Phi Uncertainty Width Transform Tool

Description

Compute phi as negative log2 of the numeric diameter in millimeters, reverse diameter extrema for phi bounds, and return logarithmic width.

Sediment and soil calculations distinguish mass basis, solid density, bulk volume, and grain-size conventions. Changing moisture or grain-size scale changes the denominator or coordinate, not the physical sample itself.

Compute phi as negative log2 of the numeric diameter in millimeters, reverse diameter extrema for phi bounds, and return logarithmic width.

When to use this tool

Use Grain Size Phi Uncertainty Width Transform when you need an explicit sediment or material-basis conversion.

How to use the tool and how it works

Enter diameterMm, minusMm, plusMm. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read phi, lowerPhi, upperPhi, phiWidth. Use the output convention below.

Require positive diameterMm and nonnegative minusMm smaller than diameter and nonnegative plusMm. Compute phi as negative log2 of the numeric diameter in millimeters, reverse diameter extrema for phi bounds, and return logarithmic width.^[1]

Input field	Meaning and units	Accepted input
diameterMm	Positive nominal grain diameter in millimeters.	Required. Finite number; strictly above 0.
minusMm	Minus Mm	Required. Finite number; minimum 0.
plusMm	Plus Mm	Required. Finite number; minimum 0.

Output field	Interpretation	Returned shape
phi	Phi	Required. Finite number.
lowerPhi	Phi at the larger diameter endpoint; size and phi order are reversed.	Required. Finite number.
upperPhi	Upper Phi	Required. Finite number.
phiWidth	Phi Width	Required. Finite number.

json

{
  "input": {
    "diameterMm": 2,
    "minusMm": 1,
    "plusMm": 2
  },
  "output": {
    "phi": -1,
    "lowerPhi": -2,
    "upperPhi": 0,
    "phiWidth": 2
  }
}

Limitations and assumptions

The phi convention uses a 1 mm reference; diameter uncertainty can become asymmetric in phi. These are supplied bounds rather than a confidence interval, and grain measurement and sampling are not validated.
Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.

Alternative or Complementary methods

Use a traceable laboratory and sampling method for the required material property. Align wet/dry basis, solid versus bulk density, grain-size scale, and interval definitions before comparing samples.

References

Calculation and input contract: geomorphology/grain-size-phi-uncertainty-width-transform — tool.io

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