Some of the links on this forum allow SMF, at no cost to you, to earn a small commission when you click through and make a purchase. Let me know if you have any questions about this.
If you use the pellet consumption table as a guide, at 300F you'll use 7.7lbs for a 7 hour cook - and considerably less if you're cooking at 225F - probably less than 6lbs. Or course, ambient temps play a role.