How to use this calculator
- Get sand, silt and clay percentages from a hydrometer or pipette test.
- Enter all three; they should total 100%.
- Read the textural class and see it marked on the triangle.
How is soil texture class determined?
The calculator applies the USDA NRCS texture triangle boundaries. For example:
- Sand: silt + 1.5 × clay < 15
- Loam: clay 7 to 27%, silt 28 to 50%, sand 52% or less
- Clay: clay 40% or more, sand 45% or less, silt under 40%
Typical conductivity is the class mean from Rawls, Brakensiek and Saxton (1982).
Worked example
With sand 40 %, silt 40 %, clay 20 %:
USDA textural class: Loam
The calculator also gives typical saturated conductivity 13.2 mm/h; drainage Well drained, good balance; group Medium (loamy).
Assumptions and limits
- Particle sizes are USDA limits; the Indian Standard (IS 1498) uses slightly different sand and silt limits.
- Conductivity is a class average; organic matter, structure and compaction change real values a lot.
Frequently asked questions
What are the 12 USDA soil texture classes?
Sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay and clay.
How do I measure sand, silt and clay?
A laboratory hydrometer test (ASTM D7928 or IS 2720 Part 4) separates particles by settling speed. A simple jar test at home gives a rough estimate.
Which soil texture is best for groundwater recharge?
Sand, loamy sand and sandy loam let water through quickly. Clay soils need recharge shafts or bores to reach permeable layers below.
References
- USDA NRCS, Soil Texture Calculator and Soil Survey Manual (2017)
- Rawls, Brakensiek and Saxton (1982). Estimation of soil water properties. Transactions of the ASAE 25(5)
- BIS IS 2720 (Part 4), Grain size analysis