A 1 Megaton warhead will give you the following results upon detonation
Thermal radiation radius (3rd degree burn): 7.27 statute miles

Air blast radius (widespread destruction): 4.47 statute miles

Air blast radius (near-total fatalities): 1.68 statute miles

Ionizing radiation radius (500 rem): 1.93 statute miles

Fireball duration: 4.5 seconds

Fireball radius (minimum): 470.25 yards

Fireball radius (airburst): 597.62 yards

Fireball radius (ground-contact airburst): 765.53 yards

Time, Distance and Shielding are your best friends when dealing with a Nuclear Warhead going off. The longer you stay in a shelter, the more radioactive decay will have occured. The further away you are from the explosion and the further your shelter is in the ground the better off you are. The denser the materials are that you us for shielding the better off you will be.

Radioactive particles can be carried by the winds for hundreds of miles, so take a look and see which way the prevailing winds are blowing for your area. Some areas of the United States may escape the fallout altogether.

No matter what the nuclear device is, the decay rates will still be the same. Obviously the bigger the device, the more radioactive particles there will be with that device.

If you are not in one of the areas that did not get hit with a high dose of fallout, you should be able to come out of your shelter after about 2 weeks. I would still recommend that you only stay out of your shelter for very short periods of time each day. Maybe 15-30 minutes a day. But this will depend on how many rads/hour the radiation level is and to check that you will need a dosimeter.