I design theatres (I'm an architect- today I was actually working on a cinema design), and we use standard chair sizes, which we get from seating manufacturers. We can get ones which have moveable arm rests (the idea is you can move them to cuddle), but generally prefer the fixed arm ones, because they are more comfortable for normal sized people. Lucky for me, there is no fat-fuck standard here in Australia, so I can keep my shitlord designs for the time being, but putting chairs at 600mm centres makes me happy knowing obeasts would never fit in them..