AWhen doing an anniversary (tier) cake, do i charge based on wedding cake serving sizes or party serving sizes?

That is all up to you.

Some people use the same charging for all cakes whether they are birthdays, weddings etc.  Some people charge more for wedding cakes.  Its really a matter of personal preference.

AThank you so much.

I think this maybe a terminology thing, but I don't know what you mean by wedding size/party sized slices.  Most people I know have dessert slices or coffee slices.  Dessert slices are 5cm x 2.5cm x 10high, coffee 2.5cm x 2.5cm x 10cm high.  It is up to the customer to decide which sized slice they want to serve their guests, or maybe I'm misunderstanding the question.

AIn the US Wilton is the standard for slice size. There website has a party size and a wedding size. The difference comes in the height of the cake. If the cake is 4" or taller than the serving size is 1" x 2" x 4" (or taller). If the cake is 2" tall then the serving size is 2" x 2" x 2".

I price cakes for all occasions the same way. But all my cakes are at least 4" tall. I don't do short cakes. I give the client a cutting guide, explain what to do and then send them on their way.

That's up to you and whether or not you want to make less money or more money.

I use the same serving size for ALL of my cakes.  1X2X4 is actually a pretty generous serving of cake.  I've made some birthday cakes that are more elaborate than some wedding cakes, why should I make less on the birthday cake, if I were to use "party servings"?  :)

I use the same serving size for my cakes as well. 

Btw. check this article about Cake Pricing - I think it's worth reading! Here is the link: http://cakesdecor.com/entries/1717-basic-principles-of-pricing-your-cakes

AThanks for all the comments. I appreciate your input.