Here's some stuff that I used in my under grade nuclear course:
http://meyerweb.com/eric/tools/gmap/hydesim.html

if u saw the movie skyline that just came out, that's a "block buster nuke" deployed by the UAV...Designed to take out somewhere around 4/5 city blocks, yield weight around 1kt. However, hollywood thinks that a really small tactical nuke does the damage of an icbm mirv (475kt), which is considered a "city buster". Remember that the nuclear material is HEAVY!!! and airborne delivery is limited. The movie with will smith as a fighter pilot (4th of july???) had a nuke in the B2 that was delivered to the alien space ship.
Taken from wikipedia:
The B61 is a variable yield, kiloton-range weapon called "Full Fuzing Option"(FUFO) or "Dial-a-yield" by many service personnel. Tactical versions (Mods 3, 4, and 10) can be set to 0.3, 1.5, 5, 10, 60, 80, or 170 kiloton explosive yield (depending on version).
The strategic version (B61 Mod 7) has four yield options, with a maximum of 340 kilotons. Sources conflict on the yield of the earth-penetrating Mod 11; the physics package or bomb core components of the Mod 11 are apparently unchanged from the earlier strategic Mod 7; however, the declassified 2001 Nuclear Posture Review [4] states that the B-61-11 has only a single yield; some sources indicate 10 kt, others suggest the 340 kiloton maximum yield as the Mod-7.


For reference the ww2 nukes were about 20kt. There's a lot that goes on in the pico seconds of a nuclear reaction. Air density, amount of structures on the ground all have impacts on what happens on the ground. Airbursts above around 1k feet are mainly for the emp/ground destruction, 60k feet is full emp effect, but no ground destruction. Fall out, well, wear lead underwear and have lead lungs.