I never looked into this, beyond looking at the hops and saying "wow".
I dump my spent grain in the woods instead of the trash, and since I started using a hop spider I have been dumping the hops in the same bucket. My wife has been salvaging spent grain and making cookies for her and I, so when I brewed this week I emptied the hop spider into a cereal bowl. For fun, I then weighed it.
Question - how much does 1.5 oz of hops grow to after brewing?