AI've used the search function and really couldn't find an answer to my question.

I know tiered cakes require cake boards underneath each tier. I've only ever done 6 and 8 inch, or 8 and 10 inch tiered cakes, which seem perfectly stable with just a center dowel. However my semester is ending soon and I'm going to have some free time so I'd like to practice doing three tiered cakes in hopes of being able to offer them in the future. Right now I stay clear of them and wedding cakes, lol.

My question though... I use Wilton pans and have bought the Wilton cake boards in the past. But my 8inch cake board is always bigger than my 8 inch cake? Not much, but just enough that I can't ice it with the cake. Is this normal? I figured they should be the same size? Could it have to do with amount of icing? I want to order them online but I don't want to waste my money if they won't be the same size!

a small gap between the edge of your cake board and your cake is desirable. This way you can cover the cake in buttercream and then use the edge of the board as a guide when running your scraper or spatula around the cake. This way, you get a very even layer of buttercream all the way around. 

Your cake is always going to shrink a little as it cools. its the nature of th emedium

AJSo my buttercream should be thick enough to then cover the entire board? Maybe that was my problem, I haven't done it in a while and back then I wasn't putting nearly as much icing on. Thank you!!

You could also just trim the cake boards to be the size of the cake.

AAre you using cake pans with straight sides, or pans that can be stored inside each other? Cake pans that are sold in most stores are made with sloping sides (so that they can be stoed more easily, I guess) which will affect the final size of your cake. For example, if you have an 8" round pan that has sloping sides, it will measure 8" across at the top of the pan, but only 7 1/2" at the bottom, so your cake comes out smaller than you expect.