My dad watched a documentary about the Germanic tribes and hasn't stopped talking about it for the last 2 hours. I know that there were a lot of tribes, but how many people lived in one tribe? Was a tribe like a big city or more like an entire state? Or how many people were considered to be germanic back then? I couldn't find any information on Wikipedia and googling for 'germanic population size' just yields a list of the different tribes.
It is very difficult, or nearly impossible, to estimate the demographic size of such population groups (BTW, recent scholars don't like the term 'tribe') in Antiquity as well as in Early Medieval Europe due to the source problems.
One possible clue can be, however, found in the battle field archaeology from that period.
How many warriors actually fought each other in the conflicts between such groups?
A paper published this year ([Holst et al. 2018]) deals with the corpus finds from one of such ancient battle fields, Alken Enge in Denmark. According to this paper, the estimated size of each army in this battle was ca. 200, more than double of the previous general assumption, at most ca. 80. On the other hand, this 'new' discovery means that the majority of previous records have hitherto actually supported the very small figures of 'barbarian' war bands consisting of not more than a hundred, rather dozens of warriors.
Of course, this figure consisted solely of (male) warriors, so women, children, and non-combatant members like slaves should be included in the actual size of the groups. Nevertheless these are almost only somewhat reliable numbers from that period.
Further References:
Mads Kähler Holst, Jan Heinemeier, Ejvind Hertz, Peter Jensen, Mette Løvschal, Lene Mollerup, Bent Vad Odgaard, Jesper Olsen, Niels Emil Søe, Søren Munch Kristiansen. "Direct evidence of a large Northern European Roman period martial event and postbattle corpse manipulation." Proceedings of the National Academy of Sciences Jun 2018, 115 (23) 5920-5925; DOI: 10.1073/pnas.1721372115