A pebble is a clast of rock with a particle size of 2 to 64 millimetres based on the Krumbein phi scale of sedimentology. Pebbles are generally considered larger than granules (2 to 4 millimetres diameter) and smaller than cobbles (64 to 256 millimetres diameter). A rock made predominantly of pebbles is termed a conglomerate.  Pebble tools are among the earliest known man-made artifacts, dating from the Palaeolithic period of human history.

Pebble is a small clast of rock.