Unified Soil Classification System

Criteria			Group Symbol	Group Name
Gravels > 50% retained on No. 4 Sieve	Clean Gravels < 5% fines	Cu ≥ 4 & 1 ≤ Cc ≤ 3	GW	Well-graded gravel
	Clean Gravels < 5% fines	Cu < 4 and/or Cc < 1 or Cc > 3	GP	Poorly graded gravel
	Gravels with Fines > 12% fines	Fines ML or MH	GM	Silty gravel
	Gravels with Fines > 12% fines	Fines CL or CH	GC	Clayey gravel
Sands > 50% of coarse fraction passed No. 4 Sieve	Clean Sands < 5% fines	Cu ≥ 6 and 1 ≤ Cc ≤ 3	SW	Well-graded sand
	Clean Sands < 5% fines	Cu < 6 and/or Cc < 1 or Cc > 3	SP	Poorly graded sand
	Sands with Fines > 12% fines	Fines ML or MH	SM	Silty sand
	Sands with Fines > 12% fines	Fines CL or CH	SC	Clayey sand
Silts and Clays LL < 50	Inorganic	PI > 7 and plots on or above "A" line	CL	Lean clay
	Inorganic	PI < 4 or plots below "A" line	ML	Silt
	Organic	PI ≥ 4 and plots on or above "A" line	OL	Organic clay
	Organic	PI < 4 or plots below "A" line	OL	Organic silt
Silts and Clays LL ≥ 50	Inorganic	PI plots on or above "A" line	CH	Fat clay
	Inorganic	PI plots below "A" line	MH	Elastic silt
	Organic	Plots on or above "A" line	OH	Organic clay
	Organic	Plots below "A" line	OH	Organic silt
Highly Organic Soils			PT	Peat