According to Ruby's BBQ, 1/3 to 1/2 pound of raw meat per person is a good estimate. For a group of 25 people, the total weight of meat to be served would be approximately 8 to 12 pounds.
Bandit BBQ prefers to think in terms of "servings," rather than the number of guests. It recommends four servings per pound for pulled or sliced meat. A full rack of ribs feeds two to three guests. It is also suggested that serving sizes be determined by the type of guest. Men and teenagers generally eat more food than children or women; this consideration may help in determining serving sizes.