I bought mine from a seller on Amazon, Davidson's, and it came as a bag of dried flowers. I'd say use 3-5 flowers for one cup initially, tweak it from there. I like my drinks strong, so I find myself adding more tea (herbal or otherwise) than recommended by the packages. Also, be careful, it stains. One last thing...you can make a VERY nice simple syrup using hibiscus. It's good for cocktails or N/A drinks as well. Toss it in a gin fizz and you have lowered blood pressure, back poarch sippin heaven in a glass. haha.
This is a 500 grams pack and says:wash 125 gr, put into 2 lt of water, boil it, put 1.5 lt in the same flower and boil it again, add 1.5 liters of water and you have 4 lt of hibiscus.