A look at my kitchen cabinet tells me this:

A package of leave gelatin contains 12 leaves (12 g total) and the whole package is good for 1 liter of liquid.

My powdered gelatin  package does not need heating, so it may not be the same as yours. There the package contains 30 g is good for  1/2 liter of liquid.

Rather than trying to go by how much the gelatin sheets weight you should go by the recommendations regarding the amount of liquid they are good for. 3 leaves of gelatin should be good for 250 ml / 1 cup of liquid (according to package). See what your powdered gelatin package says and use as much as it wants you to use for 250 ml of liquid.