I'm not entirely sure.
I'd estimate about 30-50, for presents between my two brothers and I and our parents as well as my aunt, uncle and cousins.
But we have a really small living room too, so, I might be overestimating.
We couldn't quite fit all the presents under the tree, since the tree is reasonably well low down, and we can't push presents far underneath it, so it's sort of split with half under the tree and half under a coffee table on the opposite side of the room.