You're more than likely going to need at least 1 1/2 packs for a total of 6 ounces, but u should always take 8 ounces just in case. Trust me, u don't want to be the one leaving the salon with your hair half done to go buy some more hair or waste your stylist time by showing up with only 1 pack of hair.
8 ounces isn't really a ton of hair. Most ppl going for the big hair look install 10 or 12 ounces.