I am making a passion fruit mousse, and only have gelatin sheets, not powdered gelatin which is called out in my recipe. Does anyone know if I can substitute the sheets for the powder, and how much, HELP!!!!!!

You can substitute it.
A packet of dry powdered is about 7 grams (or about 1/4 oz). Commercial sheets can range from 2-4 grams, so I would weigh it out and go from there.

Sheet gelatin usually weighs 3 grams (1/10 oz) per sheet. It always absorbs 1.5 ounces for every 9 grams (3 sheets). When fully bloomed it will absorb 5 times its weight.
To substitute sheet gelatin for powdered, submerge sheets in water, calculate amount of liquid absorbed and figure into the recipe. Then add missing water to sheets when heating to dissolve. if the recipe calls to soften 18 g of powdered in 4 oz water, substitute 6 sheets softened in enough water to cover but since they will only absorb 3 oz add 1 oz more.

To substitute powdered for sheets, use an equal weight of powder dissolved in as much water as the sheet would have absorbed. If a recipe uses 6 sheets, substitute 18 g powdered soften in the same amount of water the sheets would have absorbed-3 ounces.