you have to do the math. your total purchase will have the total weight of all the slices.
then count the slices. divide the total weight by the number of slices and that is how much each slice is.
the last time i bought mozzarella i bought 3.9 oz or .24lbs of it and it was five slices. so .24/5 is .048lbs per slice or you could do 3.5/5 to get .78oz per slice. there will be some rounding errors, but it's small enough not to make a difference.
-google first. ask questions later.