Table T1. Comparison of millimeter, phi, and Wentworth classification of grain size.
|
Grain size (mm) |
Phi (ϕ) | Wentworth grain size classification (ϕ) |
|---|---|---|
| (1 km) | –20 | |
| 4096 | –12 | |
| 1024 | –10 | Boulder (–8 to –12) |
| 256 | –8 | Cobble (–5 to –8) |
| 64 | –6 | |
| 16 | –4 | Pebble (–2 to –5) |
| 4 | –2 | |
| 3.36 | –1.75 | |
| 2.83 | –1.5 | Granule (–1 to –2) |
| 2.38 | –1.25 | |
| 2 | ||
| 1.68 | –0.75 | |
| 1.41 | –0.5 | Very coarse sand (0 to –1) |
| 1.19 | –0.25 | |
| 1 | 0 | |
| 0.84 | 0.25 | |
| 0.71 | 0. 5 | Coarse sand (1 to 0) |
| 0.59 | 0.75 | |
| 0.5 | 1 | |
| 0.42 | 1.25 | |
| 0.35 | 1.5 | Medium sand (2 to 1) |
| 0.3 | 1.75 | |
| 0.25 | 2 | |
| 0.21 | 2.25 | |
| 0.177 | 2.5 | Fine sand (3 to 2) |
| 0.149 | 2.75 | |
| 0.125 | 3 | |
| 0.105 | 3.25 | |
| 0.088 | 3.5 | Very fine sand (4 to 3) |
| 0.074 | 3.75 | |
| 0.0625 | 4 | |
| 0.053 | 4.25 | |
| 0.044 | 4.5 | Coarse silt (5 to 4) |
| 0.037 | 4.75 | |
| 0.031 | 5 | |
| 0.0156 | 6 | Medium silt (6 to 5) |
| 0.0078 | 7 | Fine silt (7 to 6) |
| 0.0039 | 8 | Very fine silt (8 to 7) |
| 0.002 | 9 | |
| 0.00098 | 10 | Clay |
| 0.00049 | 11 | (Some use 2 µm or 9 as the clay boundary) |
| 0.00024 | 12 | |
| 0.00012 | 13 |
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