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.

LL

Liquid limit in water-content percent.

PL

Plastic limit in water-content percent.

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

PI

Plasticity index in water-content percent.

• Geotechnical correlations and idealized failure models depend on stratigraphy, sampling disturbance, drainage, stress history, groundwater, density, anisotropy, scale, construction sequence, and laboratory or field method. Site-specific design requires investigation and code factors.
• 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 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.

• Activity Number Calculator

  Compute the Skempton activity A as plasticity index divided by the clay fraction finer than two micrometers, both in percent.