I'm going to attempt to cook a Pork Butt on my Green Egg for the holidays. For those of you that have done this how much charcoal should I use for a 9-12 hour low and slow (225°) cook. I use good quality lump charcoal in all my cooking now. Wish me luck.

How big is your Butt?

I use B&B and just fill it up to right at or just slightly above the fire ring and it has always been plenty.

I always fill my egg up to the fire ring. How long and hot your fire burns depends more on your air flow than how much charcoal you have. The cool thing about the egg is that it is never wasted. As soon as you shut off the intake and cap the chimney it snuffs right out.

Some good advice above. I fill mine to the bottom of the fire ring as well. Pork butt is probably the easiest/most forgiving long cooks you can do. I've switched to the "turbo butt" method recently (hot and fast at ~350 deg, indirect) and cant tell a difference between this and low and slow.

B&B filled to the top with a couple of pecan chunks.

Another reason to keep the egg full of charcoal is it is a huge PITA to add coals if you fire dies in the middle of a cook. Everything has to be pulled off the grill, deflector plate removed, etc. Start with it full and you can burn low temps for around 18 hours.

Did one couple weeks ago on the BGE 275 for 5 hrs temp probe at 175 no wrap no peaking and half the time

^^^^
This

My egg is an XL and I always fill it up.
The question is how much smoke do you want to put on the meat? And then at what point do you want to wrap it up and slow cook it the rest of the way. Depending on if you are slicing or eating pulled pork I would think makes the difference in cook time.

Coff seem like an eggspert... see what i did there?

Far cry from an eggspert. But I've F-ed up enough cooks to have learned a trick or two.

Exactly this. Using apple, cherry and hickory?

This too. No wrap, no peek will give you a nice bark that will mix into pulled pork very nicely.

I have 2 XLs and a MMX.