Abraham Lincoln once said "A man's legs should be long enough to reach from his hips to the ground."
I think the same is true of hubs - there is no one right size.
That said, if you are seeking good Google ratings, I've heard that 500 words is a minimum, and 1500 excellent.
It's more important that a hub be clear and well organized. My capsules tend to be 3 to 5 paragraphs long. And a hub could be one to six capsules.
Poetry and fiction are a totally different story. I suggest you read, and then measure the length and understand the structure of your favorite hubs.