Recommendation is 1 box per 4 hens. However, it doesnt matter how many boxes you put up-they will all want to go in the one that has a hen laying! I have 7 boxes and every day there will be many eggs in one box and only one or two in the others.
IF you haven't bought boxes yet-I highly recommend the gray plastic ones from Fleming outdoors...Fleet Farm carries them as do others. THey are about 20 each, easy to clean, and out of 4 types i tried they seem to be the favorite.
How many more hens do you plan to get? It makes a difference.
The 4 to 1 is a standard rule of thumb used on this forum. It’ll keep most of us out of trouble most of the time and is meant for small backyard flocks. If you have a lot of chickens you don’t need quite as many nests as that ratio gives you.
I always suggest a minimum of two nests even with fewer hens than you are thinking about. You can possibly get by with one when everything is going great, but the extra nest gives you some flexibility when dealing with a problem.
Most of the time they do tend to lay in the same few nests and ignore others, but what if you have a broody hen that doesn’t want to share the nest? Most broodies will allow other hens in the nest to lay with them but some won’t. Even if you don’t want her to hatch eggs it might be a few days before you can break her from being broody.
I’ve had a nest hog. She was not broody but she would stay on the nest 3 hours while she was laying her egg and would not allow any other hen on that nest.
I currently have 11 hens laying in three nests. About half the eggs are usually in one nest but they use all three. A lot of the times I’m down there during the morning I’ve seen all three in use. A couple of weeks back I saw two hens in each of the three nests at the same time. I’ve managed to let one broody hatch in this situation but if I got two broodies at the same time I’d need to add a fourth.
When you are planning your facilities don’t just think of when the weather is great and things are going great but build in a little flexibility. That makes things easier when everything is not going perfectly.
So with 4 to 6 hens, two nests should work out fine. If you get more, I’d stick with the 4 to 1 ratio unless you get a lot more hens.