A cobble is a clast of rock with a particle size of 64 millimetres (2.5 in) to 256 millimetres (10.1 in) based on the Krumbein phi scale of sedimentology. Cobbles are generally considered to be larger than pebbles (4 to 64 millimetres diameter) and smaller than boulders (greater than 256 millimetres diameter). A rock made predominantly of cobbles is termed a conglomerate.
See also 
- Folk, R.L. (1980) The Petrology of Sedimentary Rocks. Austin, Texas, Hemphill Publishing Company. 182 pp. ISBN 0-914696-14-9
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