This infographic from the National Post lists the types of rockets in the North Korean arsenals and their theoretically reliable ranges. The only thing missing is North Korea's most recent rocket, the recently launched Unha-2.
First of all, most analysts believe that North Korea is years from being able to strike the mainland U.S. with one of these, especially given proven capabilities and American defenses.
Second, North Korea is also believed to be years away from being able to place a nuclear warhead on one of these.
The U.S. State Department initially responded to the North's recent strike plan by calling it more warmongering bluster, but in the last few days America has moved two guided-missile destroyers off of the Korean peninsula.
On the other hand, North Korean threats are very serious to staunch U.S. allies Japan and South Korea, which are easily within range of these weapons.