Welcome to Hub Pages, Phelcky!
Not to be flippant or dismiss your question, but every hub and every topic is different, so I have to say a hub should be, "as long as it needs to be."
Some will require ,1500 or 3,000 words; Others can be put together with 500 or less.
It's hard to assign a hard-and-fast absolute value. It's also dependent upon each individual's writing style.
Pick topics you enjoy and know something about, and feel your way through exploring those subjects as you write. You'll soon discover what works best for you.