Pretty sure that it is 5, so you could have 4 and a Nob as hakoMike says.
In a game you should never really take squads bigger than 12 in my opinion because they can\'t mob up, so if they break you are pretty screwed and loose a big unit. Shouldn\'t take less than 8 either, because the likelihood of them passing their power of the Waagh! test gets much lower.