Table 2. Grain-size scales (soil classification). 



Wentw'orth Scale 



(Size Description) 



Phi Units 



^2 



Grain 



Diameter 



d (mm) 



U.S. Standard 

 Sieve Size 



Unified Soil 



Classification 



(USC) 



Sand 



Boulder 



Cobble 



Pebble 



Granule 



Very Coarse 



Coarse 



Medium 



Fine 



Very Fine 



Silt 



Clay 



Colloid 



-2 



-1 







1 



2 

 3 



4 

 8 



12 



256.0 

 76.2 

 64.0 

 19.0 



4.76 



4.0 



2.0 



1.0 



0.5 



0.42 

 0.25 



0.125 



0.074 



0.0625 



0.00391 



0.00024 



3 in. 



% in. 

 No. 4 



No. 10 



No. 40 



No. 200 



Cobble 



Coarse 



Fine 



Coarse 



Medium 



Fine 



Gravel 



Sand 



Silt or Clay 



1. From U.S. Army, Corps of Engineers, Coastal Engineering Research Center, 



2. <p= — logj d(mm). 



1973. 



30 



