Games : What determines the number of required voters?

Just as the title says, what determines the number of required voters?

From its help page:

Voting

There is a minimum number of players who are required for a round to count. This number starts at one (so you can in fact play on your own, if nobody else is playing), but it increases if many users are playing, and it decreases again if there aren't.

First, I believe it only counts the number of people who currently open the Stack Egg (if not, then smaller sites would have difficulties in playing). Next, it's obvious that when playing alone, the required voters is 1. Even with 2 players, the required voters is still 1. But it becomes harder to know from here. I observed that you need at least 2 voters for 3 players (but I haven't proved it, since I didn't know if there were other players). If so, then can I say that the required voters is half of current players, rounded down?