400 sq ft is just optimistic advertising .... it depends on how thin you roll on the paint, how much texture your wall has, how thirsty the wall is, and what your tolerance for white specs is.

I've found I always need a 2nd coat. Even if I press the roller into the wall really hard on the 1st coat, I'll still get white spots and I'll also get a really awful 1st coat texture/finish. So 2 coats it is. I usually go for the slightly thinner Behr Premium to save money, because thinner paint is easier to roll on and has a better finish.