The biggest goof I've ever seen made was with chicken math by a friend in California, his calculations resulted in over crowding which created a pecking order disfunction which cost him half his flock.
What we do at Buzzard's Roost is calculate both inside space and outside space, for the inside we divide by 4 to get the number of chickens possible, for the outside we divide by 12 to get the number of chickens possible. The next thing we do is use the smaller number derived as the number of chickens we can house.
We free range our chickens, this means we could have a larger number of chickens or at least the number provided by the inside space computation. However, since we are not on the farm 24/7 and therefor have them in the run while we are away, it is best to keep the numbers down to prevent chicken stress issues from overcrowding. Once we are no longer away all day, we will be able to increase the number of chooks should we so desire.