Welcome to the Cake Decorators Q&A
2 tier question
When doing a 2 tier cake, what is the recommended cake tin sizes??
The combination you choose depends on how many people are to be served. Tiers usually graduate in two inch difference for eg 6" and 8" or 8" and 10" 10" and 12". Please have a look at Paul's tutorial on stacking cakes here:
To work out portion sizes take a peek here: https://www.designer-cakes.com/portion-calculator
Hope this helps. If you need more information, please post again.