I don't know how much they hold. The ones that look like they are the right size for the number of chickens you have. :oops:
I actually have three different water bowls and they are different sizes. Even in winter I often have different aged chickens so I'm practically always integrating...
I don't use heaters, I use black rubber bowls you should be able to get at your feed store. I have a frost-free hydrant so water is pretty close by. If I set those black plastic bowls in sunlight they keep the water thawed well down in the teens Fahrenheit. That might cover a lot of your...