sedimentary particles

Sieves. A more sophisticated method makes the size of an irregular particle the diameter of a spherical particle which sinks in a viscous liquid at the same speed as the irregular particle.

American Geophysical Union system

Name	Diameter in millimeters
small boulders	more than 256
large cobbles	128–256
small cobbles	128–64
very coarse gravel	64–32
coarse grave;	32–16
medium gravel	16–8
fine gravel	8–2
very fine gravel	4–2
very coarse sand	2–1
coarse sand	1–0.5
medium sand	0.5–0.25
fine sand	0.25–0.125
very fine sand	0.125–0.062
coarse silt	0.062–0.031
medium silt	0.031–0.062
fine silt	0.016–0.008
very fine silt	0.008–0.004
coarse clay	0.004–0.002
medium clay	0.002–0.001
fine clay	0.001–0.0005
very fine clay	less than 0.0005

Wentworth system

One well-known classification of "detrital particles" was published by C. K. Wentworth in 1922.

Name	Diameter in millimeters
boulder	over 256
cobble	64 to 256
pebble	2 to 64
sand	1/16 to 2
silt	1/256 to 1/16
clay-sized particle	1/256

Udden system

Name	Diameter in millimeters
boulder	over 256
cobble	64–256
pebble	4–64
granule	2–4
very coarse sand	1–2
medium sand	0.5–1
fine sand	0.125–0.5
very fine sand	0.0625–0.125
silt	0.0039–0.0625
clay	0.00024–0.0039
colloid	less than 0.0024

Phi value

Particles are sized by the negative logarithm to the base 2 of the particle's diameter in millimeters. Users often classify particles into ½Φ classes. Some examples:

Phi scale value	Diameter, millimeters
-12Φ	4096
-8Φ	256
-6Φ	64
-3Φ	8
0Φ	1
4Φ	1/16
6Φ	1/64
8Φ	1/256

U. S Dept. of Agriculture

Name	Diameter in millimeters
stones	over 250
cobble	250–76
gravel	76–2
very coarse sand	2–1
coarse sand	1–0.5
medium sand	0.5–0.25
fine sand	0.25–0.10
very fine sand	0.10–0.005
coarse silt	0.005–0.002
fine silt
clay	less than 0.002