It all depends on the type of meat you want to cook.  It also depends on how you place and arrange the meat inside the smoke chamber.  Take pork spareribs and baby backs for example.  We’ve personally loaded up our drums with as many as 24 racks of baby back ribs before using a rib hanger.  At least 16 racks of trimmed up spareribs can fit in there for a cook.  When it comes to using grill grates you are limited to how you can place your cuts of meat inside the cooking chamber.  The space is a little more limited horizontally than vertically.  However, you can definitely fit a nice sized brisket around 17 to 21 pounds in there.  One brisket that size can feed a lot of people, especially when factoring in some sides.  You can fit as many as 4 pork butts on a grate.  And, if you don’t hang your ribs you can fit about 3 to 4 St. Louis style racks laying down on the grate.  More if you use a rib rack.  You can fit 2 to 3 whole chickens on a grate depending on their size.  More if you split them open (spatchcock), or cut the split open chickens in half, and hang them.  You can load up a couple of grates full of chicken leg quarters, drums, thighs, and or wings and cook the meat on both grates at the same time.  Find out more about how much meat can be cooked inside a drum