GRAIN SIZE SCALES 

 (Soil Classification) 



Wentworth 

 Scale 

 (Size Description) 



Phi Units 



A * 



Grain 



Diameter, 



D (mm) 



U.S. Std 

 Sieve 

 Size 



Unified Soil 

 Classification 

 (USC) 



Boulder 



Cobble 



Pebble 



Granule 



Sand 



Very Coarse 



Coarse 



Medium 



Fine 



Very Fine 



Silt 



Clay 



Colloid 



-2 



-1 







1 



2 

 3 



12 



256 

 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" 



3/4" 

 No. 4 



No. 10 



No. 40 



No. 200 



Cobble 



Coarse 



Fine 



Coarse 



Medium 



Fine 



Gravel 



Sand 



Silt or Clay 



= -log2 D (mm) 



A-35 



