Built by a geologist
USCS Soil Classification Calculator
The Unified Soil Classification System groups soils for engineering description using measured particle-size distribution, liquid limit, and plasticity index. GeoMiner turns entered laboratory index results into a transparent decision path for inorganic soil. It shows the calculated gravel, sand, fines, and coarse fractions, the exact branch selected, every required dual symbol, the assigned group symbol and name, and the limitations that remain. It is a decision aid rather than a laboratory test, standard, certificate, geotechnical design, or substitute for a complete soil description. The calculation applies to a representative sample normalized to the material passing the 75 mm or 3 inch sieve. Percent passing No. 4 and percent passing No. 200 must be dry-weight percentages from the same sample and basis. The nominal No. 4 opening separates gravel-size from sand-size material, while No. 200 separates sand-size from fines. Gravel percent equals 100 minus percent passing No. 4. Sand percent equals percent passing No. 4 minus percent passing No. 200. Fines percent equals percent passing No. 200. These three fractions must add to 100 percent. Percent passing No. 200 cannot exceed percent passing No. 4. Cobbles and boulders retained above 75 mm are outside the numeric fraction used by this calculator and must be described separately under the governing procedure. The first decision is fine- versus coarse-grained. A soil is fine-grained when 50 percent or more passes No. 200. A soil is coarse-grained when less than 50 percent passes No. 200. Exactly 50 percent therefore follows the fine-grained branch. For a coarse-grained soil, sand is the primary coarse fraction when the calculated sand percentage is at least the calculated gravel percentage. Gravel is primary only when gravel exceeds sand. This is evaluated on the total minus-75-mm sample, which is equivalent to comparing the two components of the coarse fraction. Fine-grained inorganic soils use the entered liquid limit and plastic limit. Plasticity index equals liquid limit minus plastic limit when the result is numeric. The plasticity chart compares PI with the A-line and the liquid-limit boundary at 50. A low-liquid-limit point on the clay side produces CL, lean clay; a high-liquid-limit point on the clay side produces CH, fat clay. A point on the silt side produces ML below LL 50 or MH at LL 50 and abov