I think you haven't got any replies because your question is confussing us.
Do you mean a card or plastic box which you put eggs inside...an egg carton, then egg hight
Or a nest box where the hens lay the eggs? if so a square foot will be plenty of room. Unless you have a huge breed, in which case it should be bigger
I assume you mean nest boxes. There is no hard and fast rule. Two feet seems good, as the birds have easy access and it's fairly easy access for the person collecting eggs too. Many of the commercial nesting boxes that are for sale are stacked with nest boxes above nest boxes. The birds will still fly up to higher nest boxes, but an alighting rail in front of the box helps them to do so. They can fly up to the perch and then enter the box instead of having to fly up and into the box.
Another thing to consider ... if the nesting boxes are two feet off the floor, the chickens can walk under them. That means you haven't made the coop any smaller in terms of square feet of floor space per chicken. Also food and water can be placed in that space to give them a degree of protection from rambunctious chickens and flying poop.
I didn't talk with my husband before he built a 12 box unit, 6 over 6. I am 5 feet tall and I can barely reach into the top boxes. I told him the other day he has to build me a "step" across the front of the boxes, otherwise, I am touching my underarm area to reach in to get the eggs.