It would vary greatly around here depending on the site you are digging or the part of the county you were digging.
It's not unusual to find 20+ year old roots that weigh 1/8 oz in some areas, and in others 6-8 year old roots that weigh over 1 oz.
If they get up there in that 3/4 to 1 oz range, I sure don't mind bringing them home regardless of age
I found a bunch like that on the bluff out back last year.
If drying out at 1/3 it would take around:
48 - 1 oz roots to make a pound of dry.
96 - 1/2 oz roots to make a pound of dry.
192 - 1/4 oz roots to make a pound of dry.
288 - 1/8 oz roots to make a pound of dry.
If there is 300 roots per pound, man that is a bunch of small roots.
TNhunter