Soil texture triangle

A triangle plotting three particle fractions.

Also known as: Ternary soil diagram, Particle size triangle

Historical & archaeologicalScientificStandard profile

Meanings

The soil classification diagram plotting the proportions of sand, silt and clay on a triangle.

Officially standardisedVerified fact
Plots the proportions of sand, silt and clay to give a soil's texture class.
Contexts: Technical drawing, Maps
Officially standardisedVerified fact
Uses a triangle because the three proportions always sum to one, so two of them fix the third and the diagram needs only two dimensions to show three quantities.
Contexts: Technical drawing, Maps

Visual description

An equilateral triangle divided into named regions, with three scales running along its sides.

Symmetry: none
Orientation: upright

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references.

Sources

Standard and guidance for archaeological field evaluation and excavation
Chartered Institute for Archaeologists · retrieved 2026-08-25
The professional standard for archaeological field recording in the United Kingdom, cited for recording conventions and the structure of a site archive. Practice differs between countries and between units, and records say where a convention is not universal.
Soil Survey Manual, horizon designation and texture classification
United States Department of Agriculture · retrieved 2026-08-25
The manual defining soil horizon letter designations and the texture triangle. Cited for what a designation means. Other national systems use different letters and records say where a convention is not universal.

Last reviewed 2026-08-25

Help improve this page

Meanings

The soil classification diagram plotting the proportions of sand, silt and clay on a triangle.

Officially standardisedVerified fact

Plots the proportions of sand, silt and clay to give a soil's texture class.

Contexts: Technical drawing, Maps

Officially standardisedVerified fact

Uses a triangle because the three proportions always sum to one, so two of them fix the third and the diagram needs only two dimensions to show three quantities.

Contexts: Technical drawing, Maps

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references.

Sources

Standard and guidance for archaeological field evaluation and excavation
Chartered Institute for Archaeologists · retrieved 2026-08-25
The professional standard for archaeological field recording in the United Kingdom, cited for recording conventions and the structure of a site archive. Practice differs between countries and between units, and records say where a convention is not universal.
Soil Survey Manual, horizon designation and texture classification
United States Department of Agriculture · retrieved 2026-08-25
The manual defining soil horizon letter designations and the texture triangle. Cited for what a designation means. Other national systems use different letters and records say where a convention is not universal.

Last reviewed 2026-08-25