Here is the working math for 100 guests, using the same numbers the free BBQ Calculator uses: cooked portion per person, shrinkage during the smoke, and how many whole cuts that adds up to at the meat counter.
4 pencil-cut slices per person. That's roughly 9 packer briskets at a typical 12 lb each. Buy raw weight; smoking loses 50% to shrinkage.
Pulled Pork for 100 people: about 48 lb raw
5 oz per person (a solid sandwich). That's roughly 7 pork butts at a typical 8 lb each. Buy raw weight; smoking loses 35% to shrinkage.
St. Louis Ribs for 100 people: about 64 lb raw
3 ribs per person. That's roughly 22 racks at a typical 3 lb each. Buy raw weight; smoking loses 30% to shrinkage.
Mixing meats? Most cooks do. The calculator splits servings across every meat you pick, adjusts for light or hearty eaters, adds sides math (beans, slaw, sauce, buns), and builds a fire-up-to-serve timeline for your smoker.