50 megatons TNT equivalent; ~1,570 times Hiroshima

Photo from Wikimedia Commons
Tsar Bomba
The largest nuclear detonation in human history, and hopefully ever/Events & Phenomena
On October 30, 1961, the Soviet Union detonated the AN602 hydrogen bomb, known as Tsar Bomba, over Novaya Zemlya. At 50 megatons of TNT equivalent, it was the most powerful artificial explosion ever. The fireball was 8 km in diameter, the mushroom cloud rose 67 km high, and the shockwave circled the Earth three times. Windows broke 900 km away. The bomb was originally designed for 100 megatons but was deliberately halved because even the Soviets thought that was too much.
Measurements
~8 km across; visible 1,000 km away
67 km high; well into the mesosphere
Windows broken ~900 km away; felt shockwave 1,000+ km away
~27 tonnes; had to be carried by a modified Tu-95V bomber
8 m long, 2.1 m diameter; it barely fit in the aircraft
For a brief instant; ~1.4% of the Sun's total luminosity