Find your USDA soil texture class on the soil texture triangle by entering sand, silt and clay percentages, or calculate one missing percentage.

Use percentages of the fine-earth fraction (below 2 mm) by mass, as reported by a soil lab or jar test.

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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 percentages by mass of the fine-earth mineral fraction below 2 mm, excluding coarse fragments and organic matter from this three-part texture total. They must 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.

Enter all three fractions totalling 100%, or use the missing-percentage mode to calculate 100% minus the other two. Lab results that total 98% to 102% because of rounding are scaled to 100%, and the result says so. Classification follows the USDA Soil Survey Manual texture definitions; the official NRCS calculator reference provides related triangle tools. Rounded laboratory percentages may need clarification before classification, especially near a class boundary.

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

These fractions total 100%. At 40% sand, 30% silt and 30% clay, the USDA texture class is clay loam. Texture alone does not determine drainage, fertility or plant suitability.