Here's a link to an interesting article..
http://www.space.com/scienceastronomy/planetearth/asteroid_jello_001122.html
Says the crater is 100 - 150 miles wide..
I would have to revise my estimate another power of 10....
1,000 megatons.. or .. 1 to 1.5 GIGATONS..
Thanks for the link.
That is a neat animation of the crater forming.