Well, i reckon there's many ways to do it, and there's lots of variables. if your centers are solid enough for you to handle, why not weigh out 20 of them before and after they've been enrobed to get an average weight? If you're using liquid centers, weigh the dispenser you use for liquid centers before and after dispensing to get the mass of the centers used, then weigh the finished product, and by difference calculate your chocolate use.
If you're asking, on average, what is the normal ratio of chocolate to center that folks use in general - that's pretty large range - i'd say anywhere between 30-70% chocolate
There is not nearly enough information here to answer your question.
FIRST: What are the dimensions of each piece? Something that is 25mm x 25mm by 5mm is going to take a different amount of chocolate than ones with different dimensions. Also, there is the viscosity and specific density of the chocolate to consider. All of these variables will have an effect on the amount of chocolate used to enrobe each piece.
Because of this, when I have done these exercises I have always worked backwards.
Start off with a known weight of centers, cover (hand dip, enrobe, what/however) them, and then weigh the finished pieces after they are fully crystallized. You probably want to cover 100 pieces to average out small differences. Weigh the finished pieces. Subtract the starting weight from the finished weight to get the amount of chocolate used and then divide y the number of pieces to get the average weight of chocolate on each piece..
Thank you Gordon, I totally understand your method