Most U.S. and Russian nuclear missiles have one ton or smaller nuclear warheads (actual size, not TNT equivalent yield). But, Russia also has about 70 nuclear missiles with 5-9 ton warheads, about 15 of which are land mobile, and the rest of which are in silos. Russia is phasing out these larger warhead nuclear missiles.
Presumably, the reason for this (in addition to the cost of coming up with a truly comparable replacement) is that a nuclear missile or two with a one ton warhead is more than sufficient to blow up anything that any military officer could want to blow up (we are talking entire cities here with a single missile), at least until we are invaded by technologically superior space aliens. But, any move to reduce the global nuclear weapon stockpile is still probably a good thing.