Is every book going to be bigger than the previous one?

No, definitely not, or book seven would be around the weight of a baby hippopotamus. According to the plan for book six, it will be quite a bit shorter than ‘Order of the Phoenix’. I am not going to swear on my children’s lives that that is going to be the case, but I am 99% certain of it.

J.K. Rowling has her own official web site, which I’ve never even thought to check out until today.