So you didn’t even look at the link I provided?

It lets you select the warhead size and whether it is an air burst or ground burst. Also since the Cold War ended, most countries, except china, have opted for smaller warheads and better precision. Most rogue states can only manage a fission bomb not a fusion devices, the same goes for India and Pakistan. And a fission device is what is used as a tactical nuke by the major powers. It is what Russia is threatening Ukraine with.

So the most likely device to go off now, is about the same yield of one of the original ones used on Japan.

The doomsday scenario you describe will only happen if every nuclear armed power everywhere unloads their entire arsenal all at once. If that were to happen you still will not need to worry, because you will be dead. But I put that as a very low probability event. Putin doesn’t want to die, Trump doesn’t want to die, Xi doesn’t want to die. Nobody is going to go there.