Pick a city, any city, punch in the size of your nuclear warhead, and this simulator will show you the effects of the blast.
You might also like this one from the Federation of American Scientists, which allows adjustment of charge (in kilotons) and whether the blast is delivered by automobile (surface burst, less damage) or airplane (bigger effect). Small terrorist bomb might be 20 kilotons, about what we dropped on Japan in WWII. Avg warhead = ~150. Big = 550.