Prime rib: the cut
A prime rib roast, or standing rib roast, is cut from the back of the upper rib section of the steer, and it usually comprises a total of seven ribs. To make the Slow-Roasted Prime Rib, you’ll need a three-bone rib roast, which can be cut either from the chuck end or the loin end of the rib section.
The chuck end (aka the large end or second cut) is bigger in overall size, but it has a smaller rib eye, with several thick layers of fat interspersed between portions of lean meat.
Author Suzanne Goin prefers a three-bone rib roast cut from the loin end—called the small end or first cut. It’s smaller in overall size, but it has a larger rib eye, meaning more meat and less fat.