KT, check this link. It talks abouts wraps per inch. Apparently US worsted wool should equate to 12 WPI. There are other equivalents for sport, fingering, etc. I have a pattern where the yardage of calculated by WPI (it's one o f those knit to fit you things using any needle/yarn)
Maybe if you Google worsted weight yarn in germany, you'd get some sort of equivalent. Perhaps they call it something different in Europe.
The posters here got me started on Google. I Google everything now!