When ordering ribs at a restaurant it's not uncommon to see the terms "full-rack" and "half-rack" listed. However, that often doesn't tell the person how many ribs they'll actually get.
A typical slab/rack of pork ribs is 10-13 ribs. Meaning, a half rack of ribs would contain 5 or 6 individual rib bones.
Pork ribs are sold as "slabs." For the sake of this article, you can think of this as a "full rack" of ribs.
Depending on the breed of pig, they will have 15-16 rib bones. However, when a hog is butchered, 2-3 bones are left in the shoulder, and smaller bones are also trimmed with the discretion of the butcher.
In a grocery store, you should expect to see at least 10-13 bones in a slab or "full rack" of pork ribs.
In my example above, the baby back ribs have a total of 13 ribs. If we were to turn these into "half racks" - each person would receive 6 ribs and the 13th would likely be removed as there is very little, if any meat.
Be sure to check-out my guide to smoking baby back ribs!
Fun-fact: If you have less than 10 bones, you have what's called a "cheater" rack.
When ordering from a restaurant (not a barbecue joint) the ribs you're eating are likely baby back ribs.
However, if you're eating at a barbecue joint - they will likely make the distinction and say whether or not they sell spare ribs (explained below).
In terms of serving sizes:
Baby back ribs come from the upper portion of the rib cage, where the ribs and spine meet - which is loin meat.
Pork spare ribs are taken from the bottom of the ribs or the underbelly of the hog - where the pork belly (and bacon) come from.
Spare ribs can also be St. Louis cut or "center cut." All this means is that they're trimmed to remove the sternum, costal cartilage, and flap. This process creates a more traditional "rack" of ribs.
Spare ribs are meatier and have more flavor (due to the fat content). However, they are less tender than baby back ribs which come from the loin. The pork loin is known for being a very lean cut of meat and contains very little intramuscular fat.
Rather than taking my word for it, I went to a number of different restaurant's websites to see what their menus showed.
Below is a quick breakdown:
Note: All of these restaurants sell baby back ribs.
For even further comparison, a popular BBQ joint in my area is Big Fatty's BBQ; Big Fatty's sells spare ribs not baby backs. On their menu they state the following:
*Again, Slab means rack - so a half-slab is a half-rack.
So even in terms of spare ribs, we have the same number as baby backs. The reason they say "average" is because most barbecue joints sell meat based on weight, not the number of ribs.