An old Cook's Illustrated trick was to save a card board milk carton (the bigger one) and use to measure charcoal before throwing it on. Or you could use a chimney starter to figure out how much you are using. There is always the age-old method of counting one by one (but that gets old after a time. It will take some trial and error to figure out how much charcoal yu use for different cooks depending on how much food, what temps (smoking lo 'n' slow vs grilling), and for how long you need to cook. You can also try using the charcoal basket as guides. I usually just eyeball and light it up. The performer is so air tight that I can always use the left over charcoal next time, by shutting the lid damper and bottom vents - coals go out and the grill is cold in 30-60mins.