The W76 used by the US and UK submarines is 90-100 kT. Most other US warheads are 300-475 kT (W78, W87, W88). There's apparently a small number of 5-7 kT "W76

The W76 used by the US and UK submarines is 90-100 kT. Most other US warheads are 300-475 kT (W78, W87, W88). There's apparently a small number of 5-7 kT "W76 mod 2" warheads as well. Russian warheads tend to be bigger, around 500-1000 kT, presumably to compensate for poorer accuracy.