What size tiers would look nice on a round wedding cake for 100 people plus a small tier for the bride...she wants 3 tiers but I am thinking it will have to be 4.
There's a great serving chart on this site check it out.
It's up to you and the bride but here is a reference:
Cake calculator. someone on here sent it to me...I love it!!!!
Just click your pan size or shapes...and it will tell u how many ppl...keep doing it until u get what u want total.