Baby back ribs come from the loin or right along the back on either side of the spine. They’re shorter and leaner than spare ribs. Spare ribs come from the side/belly area and are larger and meatier than baby back ribs. (St. Louis–cut ribs are spare ribs with the rib tips removed.) Spare ribs and baby back ribs can be used interchangeably in most recipes. Spare ribs take a little longer to cook, typically 2-3 hours vs. 1 1/2-2 hours for baby back ribs.