I am making a homemade wedding cake 3 tier, need to know how many cake batches I will need to make?

Look at Rose Levy Beranbaum, The Cake Bible. At the end of the book she has a very detailed helpful section on making wedding cakes, including pan sizes and recipe volumes, for both cake and icing.

If you have a standard recipe for a two layer cake, I would multiply the ingredients x 1.5 to get three layers.