That number was based on a silly division that went something like this: nb bombs (~20k) x average yield (~ 200 kT TNT) / nb people ( ~ 4 bn at the time) = 1 to

That number was based on a silly division that went something like this: nb bombs (~20k) x average yield (~ 200 kT TNT) / nb people ( ~ 4 bn at the time) = 1 ton of TNT per person, which is enough to kill you about 100 or 1000 times, pick a number.