You can get an idea of what to expect(!) from the webpage below:
Google Maps Nuke Zone

This is a Google Maps hack which allows you to map out the zones of destruction from a nuclear detonation. You can adjust the yield of the bomb and place the center anywhere you'd like. Using this I was happy to discover our house/school/workplace are all far enough away from the port of Houston to escape everything but the fallout from even a giant bomb. I figured the port of Houston would be the most likely spot for Houston to be hit via a smuggled Iranian/North Korean bomb.

Overall, the zone of destruction from an atomic bomb is suprisingly small. <img src="/images/graemlins/crazy.gif" alt="" />

-Mark