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IS 1498:1970 is the Indian Standard (BIS) for classification and identification of soils for general engineering purposes. This standard covers the classification and identification of soils for general engineering purposes based on their index properties. It establishes a unified soil classification system categorizing soils into coarse-grained, fine-grained, and highly organic soils using both laboratory tests and field identification methods.
Provides a system for classification and identification of soils based on their engineering properties and behaviour for general engineering purposes.
Quick Reference — IS 1498:1970 Soil Classification
Classification & identification of soils for engineering purposes. USCS-equivalent system used in Indian geotech reports.
✓ Verified 2026-04-28
Reference
Value
Clause
Coarse-grained — gravel (G)
> 50 % retained on 4.75 mm
Cl. 4.2 (Table 2)
Coarse-grained — sand (S)
> 50 % retained on 75 μm + < 50 % > 4.75 mm
Cl. 4.2 (Table 2)
Fine-grained — silt/clay (M/C)
≥ 50 % passes 75 μm
Cl. 4.2 (Table 2)
Well-graded gravel — symbol
GW
Cl. 4.2 (Table 2)
Poorly-graded gravel — symbol
GP
Cl. 4.2 (Table 2)
Silty gravel / clayey gravel
GM / GC
Cl. 4.2 (Table 2)
Well-graded sand — symbol
SW
Cl. 4.2 (Table 2)
Poorly-graded sand — symbol
SP
Cl. 4.2 (Table 2)
Silty sand / clayey sand
SM / SC
Cl. 4.2 (Table 2)
Inorganic silt low-plasticity
ML (LL < 35)
Cl. 4.3
Inorganic silt intermediate-plasticity
MI (LL 35–50)
Cl. 4.3
Inorganic silt high-plasticity
MH (LL > 50)
Cl. 4.3
Inorganic clay low-plasticity
CL (LL < 35)
Cl. 4.3
Inorganic clay intermediate-plasticity
CI (LL 35–50)
Cl. 4.3
Inorganic clay high-plasticity
CH (LL > 50)
Cl. 4.3
Organic silt — symbol
OL / OI / OH
Cl. 4.3
Peat / highly organic — symbol
Pt
Cl. 4.3
Coefficient of uniformity Cu (well-graded)
Cu > 4 (gravel) / > 6 (sand)
Cl. 4.2.4
Coefficient of curvature Cc (well-graded)
1 ≤ Cc ≤ 3
Cl. 4.2.4
A-line equation (PI vs LL)— separates clay from silt on plasticity chart
PI = 0.73 (LL − 20)
Fig. 1
Black cotton soil — typical classification
CH (sometimes CI)
Annex
Laterite — typical classification
ML, MI, or SM (depends on weathering)
Annex
⚠ Reaffirmed; remains the working standard for Indian soil classification. Cross-referenced by IS 6403 (bearing capacity), IS 1888 (plate load), and IS 2720 series.
! Always use the A-line chart in conjunction with liquid limit and plasticity index to accurately classify fine-grained soils into clays or silts.
! Dual symbols (e.g., SW-SM) must be used when a coarse-grained soil contains between 5% and 12% fines.
! Field identification methods like dilatancy (shaking test), toughness (threading test), and dry strength are critical for quick on-site preliminary classification.
Consolidated list per BIS. For the text of each amendment, refer to the BIS portal link above.
soilsandgravelclaysiltpeatearth
International Equivalents
Similar International Standards
ASTM D2487-17(2023)ASTM International (US)
HighCurrent
Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
Provides a nearly identical classification system based on the same USCS principles and laboratory testing.
ISO 14688-2:2017ISO (International)
MediumCurrent
Geotechnical investigation and testing — Identification and classification of soil — Part 2: Principles for a classification
Defines international principles for soil classification but uses different particle size boundaries and plasticity divisions.
BS 5930:2015+A1:2020BSI (UK)
MediumCurrent
Code of practice for ground investigations
Comprehensive UK code for ground investigations which includes a soil classification system largely based on ISO 14688.
AS 1726-2017Standards Australia (AU)
MediumCurrent
Geotechnical site investigations
Australian standard for geotechnical investigations that includes a soil classification system similar to USCS but with some local variations.
Key Differences
≠IS 1498 subdivides fine-grained soils into three plasticity groups: Low (L) for LL < 35, Intermediate (I) for 35 ≤ LL ≤ 50, and High (H) for LL > 50. ASTM D2487 uses only two groups: Low (L) for LL < 50 and High (H) for LL ≥ 50.
≠ASTM D2487 provides more explicit and mandatory rules for the use of dual symbols for borderline classifications (e.g., soils with 5-12% fines like GW-GM), whereas IS 1498 is less prescriptive about their application.
≠The naming conventions for coarse-grained soils with secondary fractions (e.g., 'sandy gravel' vs 'gravel with sand') are more rigorously defined by specific percentage ranges in ASTM D2487 compared to the more general guidelines in IS 1498.
≠ASTM D2487 is frequently updated to incorporate new research and clarifications, while IS 1498:1970 has remained fundamentally unchanged since its publication, only being reaffirmed.
Key Similarities
≈Both standards are fundamentally based on the Unified Soil Classification System (USCS), using particle size distribution and plasticity characteristics as the primary classification criteria.
≈The boundary between coarse-grained and fine-grained soils is identical in both standards, defined at 50% of material passing the 75-micron (No. 200) sieve.
≈Both standards use the 4.75 mm (No. 4) sieve as the dividing line between gravel and sand fractions within coarse-grained soils.
≈The 'A-Line' on the plasticity chart, which separates clays from silts, is defined by the same equation in both standards: Plasticity Index (PI) = 0.73 * (Liquid Limit (LL) - 20).
≈The criteria for classifying coarse-grained soils as 'well-graded' (W) or 'poorly-graded' (P) based on the coefficients of uniformity (Cu) and curvature (Cc) are identical in both standards (e.g., Cu ≥ 4 and 1 ≤ Cc ≤ 3 for well-graded gravel).
Parameter Comparison
Parameter
IS Value
International
Source
Coarse/Fine Soil Boundary
50% passing 75-micron IS Sieve
50% passing 0.075-mm (No. 200) sieve
ASTM D2487
Gravel/Sand Boundary
4.75-mm IS Sieve
4.75-mm (No. 4) sieve
ASTM D2487
Fine-Grained Plasticity Division
Low (LL<35), Intermediate (35-50), High (LL>50)
Low (LL<50), High (LL≥50)
ASTM D2487
A-Line Equation
PI = 0.73 (LL - 20)
PI = 0.73 (LL - 20)
ASTM D2487
Criteria for Well-Graded Sand (SW)
Cu ≥ 6 and 1 ≤ Cc ≤ 3
Cu ≥ 6 and 1 ≤ Cc ≤ 3
ASTM D2487
Symbol for Intermediate Plasticity Clay
CI
CL (as LL would be < 50)
ASTM D2487
Symbol for Highly Organic Soil
Pt
PT
ASTM D2487
Sand/Silt Boundary
0.075 mm
0.063 mm
ISO 14688-2
⚠ Verify details from original standards before use
Key Values7
Quick Reference Values
coarse grained soil boundary> 50% retained on 75-micron IS Sieve
fine grained soil boundary> 50% passing 75-micron IS Sieve
gravel sand boundary4.75 mm IS Sieve
low plasticity liquid limit< 35%
medium plasticity liquid limit35% to 50%
high plasticity liquid limit> 50%
dual symbol fines percentage5% to 12% fines
Key Formulas
Ip = 0.73(wL - 20) — Equation of the A-line for plasticity chart
Cu = D60 / D10 — Coefficient of uniformity
Cc = (D30)^2 / (D10 * D60) — Coefficient of curvature
Tables & Referenced Sections
Key Tables
Table 1 - Field Identification of Soils
Table 2 - Soil Classification based on Laboratory Tests