USDA Soil Texture Triangle Calculator
Enter sand, silt and clay percentages and read the USDA texture class straight off the triangle. Works for one sample or a hundred, and exports as vector.
What the soil texture triangle does
Soil texture is the proportion of mineral particles in three size fractions, and it drives an enormous amount of a soil's behaviour — infiltration rate, available water capacity, workability, shrink–swell potential, erodibility. The USDA triangle turns three percentages into one of twelve named classes so that people can talk about soils without reciting numbers.
The USDA size limits are sand 0.05–2 mm, silt 0.002–0.05 mm and clay below 0.002 mm; particles over 2 mm are gravel and are excluded from the calculation before you normalise. Note that this is the USDA scheme specifically. The FAO/ISSS and the older UK systems put the sand/silt boundary at 0.02 mm, so the same sample can carry different class names in different countries — always state which triangle you used.
Data
Paste straight from Excel or Google Sheets — include the header row and the columns are matched by name, in any order.
| # | Sand% | Silt% | Clay% | Sample(opt) | |
|---|---|---|---|---|---|
| 1 | |||||
| 2 | |||||
| 3 | |||||
| 4 |
0 rows of data
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How to read it
Clay percentage is read on the left-hand axis along horizontal lines. Silt is read on the right-hand axis along lines running down to the left. Sand is read on the bottom axis along lines running up to the left. Where the three lines meet is your sample, and the field it lands in is the texture class.
A useful anchor: loam is not equal parts of everything. It sits at roughly 40% sand, 40% silt and 20% clay, because clay-sized particles have so much more surface area that a little goes a long way. That asymmetry is why the clay-rich fields occupy so much less of the triangle than you would expect.
Who uses one
Agronomists and soil surveyors, geotechnical engineers logging test pits, hydrologists parameterising infiltration and water-retention models, environmental consultants doing contaminated-land assessments, and viticulturists and foresters matching species to site.
Common questions
- What if my three fractions do not total 100%?
- They are normalised automatically. This matters in practice because gravel and organic matter are removed before texturing, so raw lab fractions rarely total exactly 100.
- Is this the USDA triangle or the UK one?
- USDA, with the sand/silt boundary at 0.05 mm and the twelve standard classes. Quote the scheme alongside the class name in any report.