For the largest nuclear bomb ever tested (the Soviet Tsar Bomba, about 50 megatons):

  • Near-total devastation: about 20–25 miles (32–40 km) in diameter.
  • Serious blast damage: can extend 50+ miles (80+ km).
  • Broken windows: over 100 miles (160+ km) away.

These are approximate and depend on where and how the weapon is detonated.