YielixUSDA Soil Texture Triangle Calculator
Enter the sand, silt and clay percentages from one fine-earth sample to find its USDA textural class. Calculate a missing fraction from the other two, or explicitly approve proportional normalization of a small rounding discrepancy. Gravel and rock are excluded.
The 12 USDA Textural Classes
Each class covers a region of compositions, not a single recipe. Sand: the sand-rich corner; Loamy Sand: sand-rich material with more fine particles; Sandy Loam: a sandy mixture with enough silt and clay to leave the loamy-sand region.
Loam: a mixed sand–silt–clay region, including 40/40/20; Silt Loam: a silt-rich mixture outside the Silt region; Silt: the strongly silt-dominated corner with little clay. Loam does not mean equal thirds or guarantee ideal growing conditions.
Sandy Clay Loam: intermediate clay with a sandy balance; Clay Loam: intermediate clay in the central region; Silty Clay Loam: intermediate clay with a silty balance.
Sandy Clay: a clay-rich mixture with substantial sand; Silty Clay: a clay-rich mixture with substantial silt; Clay: the clay-rich region outside those two named mixtures. The verified polygons, rather than these qualitative descriptions, determine the exact cutoffs.
Fine-Earth Fractions and the Triangle Method
Use laboratory particle-size percentages by mass of mineral fine earth smaller than 2 mm. USDA sand is 0.05–2 mm, silt is 0.002–0.05 mm and clay is smaller than 0.002 mm. Exclude gravel and rock; do not enter volume percentages or sand-size subclasses as extra fractions.
The three fractions total 100%. The point is placed between sand at the lower left, silt at the lower right and clay at the apex. Its class and the plotted outlines use the same verified USDA-NRCS workbook polygons. Display rounding does not change classification.
Exact vertices are assigned before open edges using the workbook’s executable ownership rules. All touching regions are disclosed, including multiway vertices; no epsilon snapping moves near-boundary points onto an edge. For example, 20/40/40 is assigned Silty Clay and touches Clay, Clay Loam, Silty Clay and Silty Clay Loam.
Totals of 99–101% can be proportionally normalized only with approval for rounding. This preserves relative proportions, not a preferred class: an unbalanced triple has no triangle class to preserve. Original entries remain visible; every fraction edit or helper replacement clears approval. Larger discrepancies need corrected measurements.
Use Texture Alongside Measured Soil Properties
Texture alone does not determine measured available water capacity. Water retention, structure, organic matter, bulk density, coarse fragments and effective rooting depth affect the water actually available to a crop. Use measured site properties in Soil Moisture Depletion planning and verify any class-based defaults locally.
A texture name cannot establish soil acidity or a lime dose. Use laboratory buffer-test results and amendment quality with Lime Requirement planning.
Sodicity is a separate chemical diagnosis. Use the required ESP or SAR, CEC and soil measurements with Gypsum Requirement planning; a clay class alone is no reason to apply gypsum.
For longer-term management, Soil Organic Matter Build Plan explores organic-matter assumptions separately. Organic amendments can change structure and water behavior without changing the mineral particle-size class.
Inputs Explained
- Sand, silt and clay (%)
- Enter three finite mass percentages from 0 to 100, totaling exactly 100%. Use the fine-earth fraction smaller than 2 mm, excluding gravel and rock. Blank or invalid entries clear the live class.
- Calculate third percentage
- Use the button beneath the missing fraction after entering the other two. Their sum must not exceed 100%; the helper replaces only the selected fraction.
- Normalization approval
- For totals from 99% to 101% inclusive, approve proportional rescaling only when the discrepancy is due to rounding. This is never automatic, and any fraction edit clears approval. Original entries remain visible.
How This Calculator Works
Formula
Sand + silt + clay = 100%- All three fractions share the same fine-earth mass denominator.
Missing fraction = 100 − first fraction − second fraction- The two known fractions must be valid and total no more than 100%.
Approved fraction = entered fraction × 100 / entered total- Only for rounding discrepancies of at most 1 percentage point, with explicit consent. The class applies to this proportional composition.
x = silt / 100 + 0.5 × clay / 100; y = (√3 / 2) × clay / 100- Coordinates in an equilateral triangle of unit side length: sand (0, 0), silt (1, 0), clay (0.5, √3/2). SVG reverses the vertical direction and uses the same scale on both axes.
Class = owning USDA polygon at (x, y)- Test exact vertices, then open edges, then interiors; disclose every touching class. Approved normalization is classified before display division/rounding using total-scaled geometry.
Source
- Multi-Point Texture Triangle workbook (opens in a new tab), USDA Natural Resources Conservation Service — Supplies the verified 12 class polygons and edge/vertex ownership used by this calculator; optional sand-size subclasses in the workbook are outside this tool’s scope.
- National Agronomy Manual, Part 508 — Soils (opens in a new tab), USDA Natural Resources Conservation Service — Background on particle-size classes, the USDA triangle and soil properties. The plotting equations and consent rules below describe this tool’s implementation.
Assumptions
- One complete mineral fine-earth sample, with all three fractions measured on the same mass basis. Laboratory particle-size analysis is preferable when precise classification matters.
- Percentages are unit independent: Metric and Imperial selections leave entered text and fractions unchanged. Values must be finite and within 0–100 inclusive; enter 40 for 40%, not 0.40.
- Default classification requires an exact decimal total of 100%. Proportional rescaling is only an explicitly approved rounding correction for totals 99–101%, inclusive, and cannot resolve measurement uncertainty.
- The 12 broad USDA classes are used without optional sand-size subclasses. Exact shared-edge and vertex ownership follows the verified NRCS workbook rules, independently of polygon order.
- Classification uses full precision. Rounded table values may not sum to exactly 100%; they are presentation values rather than inputs to a second classification.
Worked Example
One sample with 40% sand, 40% silt and 20% clay
- Enter the fractions
Enter Sand 40, Silt 40 and Clay 20. Percentages do not change with metric or imperial selection.
- Check the total
40 + 40 + 20 = 100%, so normalization is unnecessary.
- Read the class
The composition is inside the verified USDA Loam region.
USDA textural class: Loam.
How to Interpret Your Results
| Condition | What It Means |
|---|---|
| Point and shaded triangle region | The marker shows the current composition; shading identifies its assigned polygon. The primary text answer and fraction table repeat the chart data. On small screens the labeled chart scrolls with keyboard focus while the summary and table remain readable. |
| Named USDA class | A description of particle-size proportions, not a measurement of fertility, soil structure or water storage. |
| Shared class boundary | All touching class names are disclosed. The NRCS workbook rules select one owner; small measurement changes can select an adjacent class. |
| Approved normalization | The displayed composition totals 100% before display rounding. The unbalanced original input has no class to preserve. |
Limitations and Cautions
- Laboratory uncertainty near a boundary can change the assigned class. Extra decimal places or normalization do not make rounded measurements more accurate.
- Different national classification systems and optional USDA sand subclasses may use different names; this tool reports the 12 broad USDA classes only.
- One sample describes the sampled material. It does not capture field variability or different soil horizons.
- Texture alone does not determine drainage, compaction, fertility, hydraulic conductivity or amendment rates.
Common Mistakes to Avoid
Including gravel in the denominator
Use sand, silt and clay percentages of the fine-earth fraction only.
Treating texture as available water capacity
Use measured water-retention properties and rooting depth for irrigation planning.
References
- Multi-Point Texture Triangle workbook (opens in a new tab), USDA Natural Resources Conservation Service — Supplies the verified 12 class polygons and edge/vertex ownership used by this calculator; optional sand-size subclasses in the workbook are outside this tool’s scope.
- National Agronomy Manual, Part 508 — Soils (opens in a new tab), USDA Natural Resources Conservation Service — Background on particle-size classes, the USDA triangle and soil properties. The plotting equations and consent rules below describe this tool’s implementation.
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