I looked thru Scotts book and found on page 92 where he mentions that around 285 roots per dry pound is about average for wild seng.
Again I am sure that varies quite a bit at different locations.
I know for sure (based on pictures I have seen posted here) that the seng roots that Billy and Chieftan and those guys harvest up in the mountains average larger than the ones we harvest down here in Middle TN.
I expect we average more like 300-350 roots per pound here where Billy and Chiefton may average more like 200-250.
There was no real difference in the price offered for our roots vs theirs though - at times our buyers were offering more for our roots than they were being offered for the larger mountain roots.
I think TNhunter is right on. When I sold mine last year, I believe it took around 350 roots for me to make a pound. I will tell you that my roots weren't nearly as big as those mountain roots Billy sometimes dug.