Pebbles on a shingle beach in Somerset, England

Pebbles on a beach at Broulee, New South Wales, Australia

A pebble is a piece of rock with a particle size of 4 to 64 millimetres. They are often made of flint.

Pebbles are 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.