The bird bath is 21 inches across, so I would make the hawk like 17 inches from beak to the end of the tail, wingspan maybe 28 inches.
I searched the blog for "hawk", we first saw the Cooper's Hawk Thanksgiving of 2007. I wonder if it's the same bird or a descendant. Cool. Cornell Lab Of Ornithology has a great bird book, which says oldest known Cooper's Hawk was 20 years and 4 months old -- so I'd guess that it's the same bird.
Hmmm, the article says that if you don't want the hawk using your bird feeders as a hunting ground to take them down for a few days and the hawk will "move on". I doubt that would work. I've seen this guy all over our neighborhood, we'd probably all have to coordinate to get him to move on. Plus, seems like he lives here, just as we do. Oh well. The article says he mostly likes bigger birds and lists starlings first, so more power to him.