Use this geological calculation for a transparent first-pass interpretation of measured rock, soil, fluid, well, stratigraphic, isotopic, geophysical, or seismic data under an explicitly selected model.

PI

Plasticity index in percent.

Clay

Clay fraction (finer than 0.002 mm) in percent of dry mass.

Compute the Skempton activity A as plasticity index divided by the clay fraction finer than two micrometers, both in percent. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

A

Activity number (dimensionless).

• Geological models are scale-, site-, method-, and calibration-dependent. Heterogeneity, anisotropy, sampling, diagenesis, pressure-temperature history, instrument response, boundary conditions, and empirical-correlation range can dominate the result.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Compare independent measurements and models, retain units and analytical metadata, propagate uncertainty, and validate interpretations against logs, cores, maps, laboratory data, or field observations.

• Atterberg Plasticity Index Calculator

  Compute the plasticity index PI as liquid limit minus plastic limit, both in water-content percent.

• Atterberg Consistency Index Calculator

  Compute the consistency index CI = (LL - w) / PI from liquid limit and natural water content in percent and the plasticity index.

• Atterberg Liquidity Index Calculator

  Compute the liquidity index LI = (w - PL) / PI from natural water content and plastic limit in percent and the plasticity index.