They need food and water so that takes the 4x4= 16 sq ft down a bit. I personally think they need at least a 4x8 brooder for anything from 12 to 20 chicks. I know a lot depends on how long they will be needing to stay in the brooder. If it is only for a month than less space is needed but if they are in it for 2 months or more they need more space since they are bigger.
Also a 4x4 brooder does not give much space to get out from under the heat lamp if some are getting to warm.
Also a 4x4 brooder does not give much space to get out from under the heat lamp if some are getting to warm.
Just my opinion.You say that 12 chick will quickly out grow a 4X4, what size do you recommend have seen 1 square foot per bird.........