Is a pebble technically smaller then a stone?

The stone is a unit of measure equal to 14 pounds avoirdupois.
https://en.wikipedia.org/wiki/Stone_(unit)

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 to be larger than granules (2 to 4 millimetres diameter) and smaller than cobbles (64 to 256 millimetres diameter).
https://en.wikipedia.org/wiki/Pebble

Stone is not a term that refers to a specific size of rock. In order from largest to smallest, these terms are: boulder (over 256 mm); cobble (between 64 and 256 mm); pebble or gravel (between 4 and 64 mm); granule (between 2 and 4 mm)sand (62.5 micrometres to 2 mm); silt, clay or mud (smaller than 62.5 micrometres).

https://en.wikipedia.org/wiki/Grain_size