The Russian nuclear forces are dependent upon her ICBM's. Her boomer subs and air force wouldn't get much launched (her bombers wouldn't make it to American airspace and her max of two deployed nuke boomers are trailed at all times by at least one American and one other NATO attack sub -- they'd never make it to launch depth). But that doesn't matter. Even if only the two modern MIRV equipped ICBMs work (the very advanced, RS-24 Yars; and the reasonably advanced RT-2UTTKh Topol-M), that would be a total of about 125 ICBM's. (trust that the aging RT-2pms, UR-100Ns and R-36 still have some bite).
All things considered, that means that the minimal (stress on the "minimal") strike would look something like this:
There are approximately 40-50 RS ICBMs. Each has between 4-8 warheads, with between 100-300kt explosive blast each warhead. Assume the average -- 6 MIRVs at 150kt blast each (7x Nagasaki), would mean 270 strikes.
There are approximately 80 RT-2UTTKh ICBMs. Each has only one warhead, but at a devastating 800kt. (40x Nagasaki), total of 80 strikes.
The total number of warhead blasts in the US would be no less than 350 nuclear strikes (that's NO LESS than, but highly likely much higher when older warheads are added in). Even if only 350 nuclear strikes occurred, and only 100 highly important targets were selected (doubling or trippling up on important locations), easily the top 80 largest cities (every major metro area) + the 20 most important military targets were struck, the US would be wiped off the face of the map. The entire nation would end. Most people would be dead in six months due to disease and starvation. If ONLY the Russians struck (with no retaliation from the US), humanity might survive such an attack.
===Total yield: 3,500 times Nagasaki (this excludes many other older nukes that, if they worked appropriately, would push this number way beyond 10,000 times Nagasaki).
The American strike would be more thorough both for Russia and possibly for humanity. The US's nuclear triad (ICBMs, Air Force and Navy) would have more successful launches due to the larger nature of the American forces and the more modern equipment. The Ballistic Missile Submarines (boomers) would do the trick, 14 total with nukes, seven deployed at any given time. They're beyond deadly. Their nuclear payloads capable of being launched in under 30 minutes.
Each Ohio Class boomer has 24 Trident II SLBM that are MIRV'ed with between 6-8 W76 110kt nuclear warhead (5.5 times Nagasaki). Even if we went with the average (7 warheads), that's 1,176 nuclear strikes from the Ohio Class nuclear payload.
The US also operates 450 Minuteman III ICBMs that are MIRV'ed with 3 nuclear warheads (in the process if not concluded, the downgrade to 1 MIRV each). The exact type of warhead is classified, but the warheads are either the W78 or W87, with no less than 300kt of explosive yield (15x Nagasaki). That's a total maximum of 1,350 nuclear warheads, minimum of 450.
The total number of blasts would be insane, no less than 2,526. We haven't even counted any Air Force method, presuming that the Russians could/would destroy them in flight. Nevertheless, even if strikes were doubled and/or tripled up on cities, it would mean that no less than 1,000 locations would be wiped out by more than one (some with three or four) nuclear blasts. The destruction would be absolute.
===Total yield: no less than 30,000 times Nagasaki
