World Library  
Flag as Inappropriate
Email this Article

Grain size

Article Id: WHEBN0031367277
Reproduction Date:

Title: Grain size  
Author: World Heritage Encyclopedia
Language: English
Subject: Wash load, Albert Atterberg, Shear strength (soil), Nintoku Seamount, Darcy's law
Publisher: World Heritage Encyclopedia

Grain size

Wentworth grain size chart from United States Geological Survey Open-File Report 2006-1195

Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which is the size of a single crystal inside the particles or grains. A single grain can be composed of several crystals. Granular material can range from very small colloidal particles, through clay, silt, sand, and gravel, to boulders.

Krumbein Phi Scale-United States

Size ranges define limits of classes that are given names in the Wentworth scale (or Udden-Wentworth) used in the United States. The Krumbein phi (φ) scale, a modification of the Wentworth scale created by W. C. Krumbein[1] in 1937, is a logarithmic scale computed by the equation



\phi is the Krumbein phi scale,
D is the diameter of the particle, and
D_0 is a reference diameter, equal to 1 mm (to make the equation dimensionally consistent).

This equation can be rearranged to find diameter using φ:

D=D_0 \times 2^{-\phi}\,
φ scale Size range
Size range
(approx. inches)
Aggregate name
(Wentworth Class)
Other names
−8 < 256 mm < 10.1 in < Boulder
−6 to −8 64–256 mm 2.5–10.1 in Cobble
−5 to −6 32–64 mm 1.26–2.5 in Very coarse gravel Pebble
−4 to −5 16–32 mm 0.63–1.26 in Coarse gravel Pebble
−3 to −4 8–16 mm 0.31–0.63 in Medium gravel Pebble
−2 to −3 4–8 mm 0.157–0.31 in Fine gravel Pebble
−1 to −2 2–4 mm 0.079–0.157 in Very fine gravel Granule
0 to −1 1–2 mm 0.039–0.079 in Very coarse sand
1 to 0 ½–1 mm 0.020–0.039 in Coarse sand
2 to 1 ¼–½ mm 0.010–0.020 in Medium sand
3 to 2 125–250 µm 0.0049–0.010 in Fine sand
4 to 3 62.5–125 µm 0.0025–0.0049 in Very fine sand
8 to 4 4–62.5 µm 0.00015–0.0025 in Silt Mud
10 to 8 1-4 µm < 0.00015 in Clay Mud
20 to 10 1-1000 nm < 0.000039 in Colloid Mud

In some schemes, gravel is anything larger than sand (comprising granule, pebble, cobble, and boulder in the table above).

International scale

ISO 14688-1, establishes the basic principles for the identification and classification of soils on the basis of those material and mass characteristics most commonly used for soils for engineering purposes. ISO 14688-1 is applicable to natural soils in situ, similar man-made materials in situ and soils redeposited by man.[2]
ISO 14688-1[3]
Name Size range (mm)
Very coarse soil Large boulder LBo >630
Boulder Bo 200 – 630
Cobble Co 63 – 200
Coarse soil Gravel Coarse gravel CGr 20 – 63
Medium gravel MGr 6.3 – 20
Fine gravel FGr 2.0 - 6.3
Sand Coarse sand CSa 0.63 - 2.0
Medium sand MSa 0.2 - 0.63
Fine sand FSa 0.063 - 0.2
Fine soil Silt Coarse silt CSi 0.02 - 0.063
Medium silt MSi 0.0063 - 0.02
Fine silt FSi 0.002 - 0.0063
Clay Cl ≤0.002


An accumulation of sediment can also be characterized by the grain size distribution, called sorting. According to a formula[4] the sorting can be quantified as

φ < 0.35 0.35 < φ < 0.50 0.50 < φ < 0.71 0.71 < φ < 1.00 1.00 < φ < 2.00 2.00 < φ
very well sorted well sorted moderately well sorted moderately sorted poorly sorted very poorly sorted

See also


  1. ^ Krumbein, W. C.; Aberdeen, Esther (April 1937). "The Sediments of Barataria Bay". Journal of Sedimentary Petrology 7 (1). Retrieved 11 May 2014. (subscription required (help)). 
  2. ^
  3. ^ ISO 14688-1:2002 at
  4. ^ Folk, Robert L.; Ward, William C. (1957). "Brazos River bar: a study in the significance of grain-size parameters". Journal of Sedimentary Petrology 27 (1): 3–26.  

External links

  • R D Dean & R A Dalrymple, Coastal Processes with Engineering Applications (Cambridge University Press, 2002)
  • W C Krumbein & L L Sloss, Stratigraphy and Sedimentation, 2nd edition (Freeman, San Francisco, 1963).
  • J A Udden, "Mechanical composition of clastic sediments", Bull. Geol. Soc. Am. 25, 655-744 (1914).
  • C K Wentworth, "A scale of grade and class terms for clastic sediments", J. Geology V. 30, 377-392 (1922).
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.