Based on the use of my Mr. Iced Tea (from Joe DiMaggio and the makers of Mr. Coffee), I'd use between 6 - 10, depending on how strong (or weak) you want your tea and the nature of the brewing process you are using. In the Mr. Iced Tea, I use 4 bags to make enough to fill the supplied 1/2 gallon container. Of course, depeinding on the type of tea you are using, YMMV. This info is based on standard Lipton supermarket bags.
Steve Z.
“Only the pure in heart can make a good soup.”
― Ludwig van Beethoven