Enter at least two of the three soil texture percentages (sand, silt, and clay) into the soil texture triangle calculator. The remaining percentage can be calculated so the total equals 100%, then the USDA soil texture class is determined from the soil texture triangle.

Soil Triangle Calculator

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Soil Triangle Formula

A soil texture triangle does not use a single formula to produce one “soil composition” value. Instead, the key relationship is that the three texture fractions sum to 100%:

Sand\% + Silt\% + Clay\% = 100\%

Variables:

  • Sand (%), Silt (%), and Clay (%) are the particle-size fractions of the soil sample, expressed as percentages (by mass), and they should sum to 100%.
  • If one fraction is unknown, it can be calculated as: Unknown (%) = 100% − (the other two fractions).
  • The output of a soil texture triangle is a USDA soil texture class (e.g., loam, clay loam), determined by plotting the three percentages on the triangle.

To classify soil texture, measure or enter the sand, silt, and clay percentages (ensuring they sum to 100%). Then plot the point on the soil texture triangle (or use this calculator) to determine the corresponding USDA texture class.

What is a Soil Triangle?

A soil triangle, also known as a soil texture triangle, is a diagram that is used by soil scientists and geologists to visually classify soils based on their proportion of sand, silt, and clay particles. The triangle is divided into various sections, each representing a different type of soil, such as loam, sandy clay, or silty clay. The three sides of the triangle represent the percentage of sand, silt, and clay, respectively. By plotting the percentages of these three components, one can determine the soil’s texture class. This classification is important as it helps in understanding the soil’s properties, such as its water-holding capacity, nutrient availability, and its suitability for different types of plants or crops.

How to Calculate Soil Triangle?

The following steps outline how to calculate the Soil Triangle:

  1. First, determine the percentage of sand in the soil sample (%).
  2. Next, determine the percentage of silt in the soil sample (%).
  3. Next, determine the percentage of clay in the soil sample (%).
  4. Verify the percentages sum to 100% (calculate the missing fraction if needed), then plot sand, silt, and clay on the Soil Texture Triangle graph to find the USDA texture class.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Percentage of sand (%) = 40

Percentage of silt (%) = 30

Percentage of clay (%) = 30