I'm a little confused with all these "serving size charts" I've seen on the internet. 

For example, this one:

https://www.google.com/search?q=cake+serving+size&rlz=1C1GCEA_enUS835US835&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjFo_LK9evgAhWXn4MKHURzAbwQ_AUIDigB&biw=1128&bih=1038#imgrc=RwN-dYYo1QhrVM:

Does the amount of servings per cake increase when you add another layer of cake? For example, would a 4-layer 8-inch cake serve more than a 2-layer 8-inch cake? If so, by how much?

Just wondering what your serving size suggestions are...

typically servings are determined by the footprint of the cake not the height

Thank you! I've been doing some more research. 

Remember most dessert plates are small and the taller cakes don’t fit well   When a “double barrel “ cake is Used there is a cake circle between the 2 tiers & they are taken apart and served as 2 separate caked so your serving count doubles   So your 4layer cake If put together as I describe above will serve (I think) 50 not just 25 

Ditto what the Cake Queens said! 

sandra, you are so funny -- i'm thinking oh we gotta new member, cakequeens -- so I go looking and no -- too funny hahahaha

Oh good grief, you know you and Lynne are my heroes, Kate!  The two of you know everything!

I wish