Soil Texture Triangle
Classify soil texture using the USDA texture triangle from sand, silt, and clay percentages. Estimates drainage, water holding capacity, and permeability.
About this calculator
The USDA soil texture triangle, defined in the USDA NRCS Soil Survey Manual (USDA Handbook No. 18, Chapter 3), sorts any soil into one of twelve textural classes based on the relative shares of sand (0.05-2.0 mm particles), silt (0.002-0.05 mm), and clay (under 0.002 mm) it contains. This calculator first normalizes whatever three percentages are entered so they sum to exactly 100% -- if a lab report's numbers are slightly off from rounding, the Normalized Sand/Silt/Clay outputs correct for that before classification runs.
The classification itself follows the general shape of the official USDA decision tree (for example, 40%+ clay reads as Clay-family soils, and the broad 7-27% clay / 28-50% silt / 23-52% sand region reads as Loam), though this implementation is a simplified approximation of the full triangle rather than a literal reproduction of every boundary in the USDA Soil Survey Manual -- for legal or engineering-grade classification, confirm against a lab hydrometer analysis and the official triangle. Water Holding Capacity and Permeability are rough estimates derived from the same three percentages: clay's small particle size and high surface area give it the highest water-holding weight of the three, while sand's large particles and open pore structure give it the highest permeability and the lowest water-holding weight.
Inputs
Results
Texture Classification
Loam
Figures current as of 2017. Source: USDA NRCS Soil Survey Manual (USDA Handbook No. 18), Chapter 3, Examination and Description of Soils
How to Use This Calculator
- Enter the percentages of sand, silt, and clay from a hydrometer analysis or lab test.
- The three percentages are normalized to 100% automatically, so small rounding differences from a lab report don't need to be corrected by hand.
- Review the USDA Soil Texture Class determined by the triangle classification.
- Check the Water-Holding Capacity and Permeability ratings for your texture class.
- Use the Texture Class output to select appropriate irrigation scheduling and tillage practices.
What each input means
- Sand Percentage
- Percentage of sand-sized particles (0.05–2.0 mm). Determined by sieve analysis or hydrometer test.
- Silt Percentage
- Percentage of silt-sized particles (0.002–0.05 mm). Sand + Silt + Clay are normalized to 100% automatically, so they don't need to sum to exactly 100% as entered.
- Clay Percentage
- Percentage of clay-sized particles (< 0.002 mm). Clay strongly influences nutrient retention and drainage.
How this is calculated
Worked example, using the default values
- Identify Input ParametersSand Percentage = 40, Silt Percentage = 40, Clay Percentage = 20 = 3 input(s) provided
- Calculate Texture ClassificationTexture ClassificationLoam = Loam
- Calculate Normalized Sand40 = 40
- Calculate Normalized Silt40 = 40
Figures and sources
- USDA soil texture triangle classification (2017) — USDA NRCS Soil Survey Manual (USDA Handbook No. 18), Chapter 3, Examination and Description of Soils
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why do sand, silt, and clay percentages need to add up to 100%?
Soil texture is defined entirely by the relative proportions of these three particle-size classes -- there is no fourth category. This calculator normalizes whatever three numbers are entered so they sum to exactly 100% before classifying, which means small rounding differences from a lab report (say, 41-39-21 instead of a clean 40-40-20) do not change the result, since only the ratios between the three matter.
What makes clay soil drain more slowly than sandy soil?
Clay particles are microscopic (under 0.002 mm) and pack tightly with very small pore spaces between them, which physically restricts how fast water can move through -- this calculator estimates permeability as low as 0.06 in/hr for clay-dominant soils versus up to 6.0 in/hr for sand-dominant soils. Sand particles are far larger and leave wide, well-connected pore spaces that water passes through quickly, which is also why sandy soils hold much less water for plant roots to draw on between irrigations.
How much more water can a clay-heavy soil hold compared to a sandy soil?
In this calculator's estimate, clay contributes roughly 7.5x more to water-holding capacity per percentage point than sand does (a weighting of 0.15 in/ft per percent for clay versus 0.02 for sand), so a predominantly clay soil can estimate several times the available water per foot of a predominantly sandy soil at the same depth. That is a rough planning estimate, not a substitute for a lab-measured available water capacity.
Is a Loam classification always the ideal soil texture?
Loam is often cited as favorable because it balances drainage and water retention, but "ideal" depends on the crop and irrigation setup -- a sandy loam that drains fast suits crops sensitive to waterlogging, while a heavier clay loam that retains more water can reduce irrigation frequency for others. This calculator reports the texture class and its drainage/water-holding estimates; deciding whether that's ideal is site- and crop-specific.
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