When determining the number of poultry drinkers needed for an automatic watering system, you'll need to know two things; the number of chickens you plan to house, and how many birds can safely drink off of one drinker.
I’m sure that in the commercial poultry production world, there is a science based formula to determine how many cups are needed for a specified number of chickens. For me to be comfortable, I’d rather speak from experience. The thing is this- unless they’ve been without water for a while, chickens are good about taking turns drinking. Unlike feeding time when everybody crowds around the feeder, taking sips of water is a casual event that happens several times a day.
Our layer pen has approximately 15 adult birds. The pen itself has only one drinker cup. It may seem that one cup is not enough for that many birds, but in reality, it is. The flock has been in that pen for over a year with just one drinker cup.
Now, I’m not interested in finding the limit, so I’ll just say 15 birds per drinker is the maximum. Depending on the size of your birds and your particular climate, my official recommendation is 10 birds per cup.
I hope this helps!