How big is a cobble?

I've missed some of the nomenclature but the ones that I do remember and their diameters are:

Boulder +250MM

Cobble 75-250 mm

Stone 25-60 mm

Pebble 4-64 mm

Gravel 2-75 mm

Sand 0. 062 -2 mm

Like the Arabic "rotl" the terms are user based. A cobble is apparently the size rock that you can pick up and support with one hand while placing it.