Free USCS & AASHTO Soil Classification Calculator

The ASTM D2487 soil classification system, an ASTM adaptation of the Unified Soil Classification System (USCS), and AASHTO M 145 are widely used methods for classifying soils for geotechnical engineering purposes. These systems classify soils based on factors including particle-size distribution, liquid limit, and plasticity index, helping geotechnical engineers, laboratories, and construction professionals consistently classify soils for design, testing, and reporting.

This USCS Calculator functions as a soil type calculator, allowing you to determine the appropriate soil group name and USCS symbols from your field data. It simplifies USCS soil classification for use in soil descriptions, geotechnical reports, boring logs, and test pit logs. For more information, you can refer to the official USCS guidelines.

Enter your soil test data below to instantly determine the USCS classification, AASHTO classification, and soil description using our free soil classification calculator.

What is the USCS Soil Classification Calculator?

The USCS Soil Classification Calculator helps geotechnical engineers, construction materials testing laboratories, and field technicians classify soil according to the Unified Soil Classification System (USCS). By entering the particle size distribution and Atterberg Limits, the calculator determines the appropriate soil group in accordance with ASTM D2487. This USCS calculator simplifies the soil classification process and provides consistent results for engineering projects.

How does the Soil Classification System work?

The soil classification system groups soils based on grain size distribution and plasticity characteristics. The Unified Soil Classification System evaluates gravel, sand, fines content, liquid limit, and plasticity index to determine the appropriate soil group. Engineers commonly use this method during geotechnical investigations, foundation design, and construction quality control.

What’s the difference between ASTM D2487 (USCS) and AASHTO M 145

ASTM D2487 (USCS) and AASHTO M 145 both classify soils using properties such as particle-size distribution, liquid limit, and plasticity index, but they serve different purposes. ASTM D2487 uses the Unified Soil Classification System (USCS) and is commonly used for general geotechnical engineering and soil descriptions, while AASHTO M 145 classifies soils primarily for highway and transportation applications, particularly their suitability as subgrade materials. ASTM D2487 assigns USCS symbols such as GW, SP, CL, and CH, whereas AASHTO M 145 uses groups A-1 through A-7 and a Group Index (GI) to help indicate expected subgrade performance.

Understanding USCS Symbols

The calculator returns standard USCS symbols that identify soil groups. Common examples include:

Gravels

• GW – Well-graded gravel
• GP – Poorly graded gravel

Sands

• SW – Well-graded sand
• SP – Poorly graded sand

Silts & Clays

• ML – Silt
• CL – Lean clay
• MH – Elastic silt
• CH – Fat clay