North Korea's latest nuclear weapons test is much more powerful than the previous two, according to estimates made by instruments that measure seismic waves from the blast. It's about the size of the bomb that devastated Hiroshima in World War II.
But it's not so easy to verify the claim that the nuclear explosive has also been miniaturized. That's a critical claim because a small warhead would be essential if the rogue regime chose to threaten the United States with a nuclear-tipped missile.
Big bombs are easier to make, but they aren't all that useful as a threat.