All depending on how you aplly it. If you do it like Taylor D. Itll be some where in the ball park of 70 sq. ft. You also have to take into consideration how you apply it. What areas you cover, wether or not you place strip over the seams, & so on. Youll use a whole sheet just to put it on the trunk lid. Or you can just put it in the tear drops on the trunk lid. I also dynamat the enitre liscense plate. If that still rattles then Ill by some 1/4" foam padding and place that in between. Now if you are doing them in strips you could use the 36 sq ft. That way is easier, cheaper and still some what effective. Of course the more you cover the better it will be. Also once you do this youll find more rattles else where in the trunk area. Once I couldnt take car of the rattle cause it was from the heat sheild over the muffler. There is a product for the spoiler that you can use if that is what is rattling. I forgot the exact name of it, but will post it once I find out.
'98 SLE - Bone Stock