Since this varies so much, it’ll depend on a few factors: temperature, grill type, and time. Hitting your target temperatures depends on fuel level: more charcoal, more heat. This rule also applies to airflow. Since oxygen availability determines how hot your charcoal burns, this is where the type of smoker or grill you’re using comes in to play (e.g. a standard upright charcoal grill is built for air exchange, and therefore hotter heat). Then, there are ceramic grills — with such reduced airflow, they’ll need less charcoal and it’ll last much longer during long cooks. It’s not outrageous for even a small charcoal load to last 16 hours or more in a kamado grill. If we were to pick one takeaway for you, we’d say: always keep extra fuel on hand. Start with a reasonable amount; when you monitor temperature, airflow, and fuel, you might find you need to add more. As you gain experience with your grill, you’ll quickly zero in on gauging your usual needs.