Castle Bravo was the most powerful nuclear device ever detonated by the United States, with a yield of 15 Megatons. That yield, far exceeding the expected yield of 4 to 6 megatons, combined with other factors, led to the most significant accidental radiological contamination ever caused by the United States.
In terms of TNT tonnage equivalence, Castle Bravo was about 1,200 times more powerful than the atomic bombs which were dropped on Hiroshima and Nagasaki during World War II. The largest nuclear explosion ever produced was a test conducted by the Soviet Union several years later, the ≈50 MT Tsar Bomba.
Extract from the movie "Trinity and Beyond"