What is the current amount of players allowed per alliance in campaigns?

AngryPenguin

Iriidius wrote: »

A few month ago at noon there was a PuG with 12 players(I got invited, unusual that full PuGs exist in empty campaign) and about 3 randoms taking an outpost and another 4 players at base whith no action and probably no players anywhere else so 19 players and 1 bar. Shortly after it switched to 2 bars so it seems to be 20 players per bar.

It's 20 players/bar. That's why it seems that way.

Zabagad

Iriidius wrote: »

A few month ago at noon there was a PuG with 12 players(I got invited, unusual that full PuGs exist in empty campaign) and about 3 randoms taking an outpost and another 4 players at base whith no action and probably no players anywhere else so 19 players and 1 bar. Shortly after it switched to 2 bars so it seems to be 20 players per bar.

Maybe you are right and have luck with your assumption, but this: "and probably no players anywhere else" sounds like something with a very low chance...
You never know if nobody is questing (I would do that in an empty campaign), riding somewhere around, looting chests/shyshards - even if your alliance held no keep/outpost/city where always some are scouting or whatever they do.