How much "grass" should I put in brownies?

Me and two of my friends are going to a concert on my birthday and I wanted to make brownies. I was planning on picking up 1/2 oz, but I was wondering how much "trees" I should actually put in the mixture. Obviously I won't put 1/2 oz, but I was wondering how much I should put in to get us ****** up, but not too ****** up