Depends on the size of the butts. Most of the butts that I get are between 7 and 8 pounds. I can easily get 4 per shelf. If they get any bigger than that, it gets a little crowded. When I do a big load, it seems to add to the cooking time. You are putting a lot of cold in there to start with. I load the biggest ones one the bottom shelf because it's the hottest. Next biggest on the top shelf. They prolly won't all get done at the same time. I stick some remote thermometers in some of them to monitor temps, then foil to cooler as the get done. I don't foil til then.