For some reason I always get confused about this...that if you have a 10" cake use a 10" board w/a 10" box. Do I have that correct. Or should you go up one size for the board and box, i.e. 10" cake, 12' board? Ive got a 10" cake here but it seems like the board doesnt allow much room for placing a border on the bottom. I know for a tied cake, the top tier boards should be as big as the cake so to hide the board once its stacked. So, what is the general rule?
For stablility I'd use the same size board but if you are leaving the cake on a board and want to decorate it you'd go up to the next size board so as to leave room for your decorations. Box, you'd want bigger than the size of the cake or your cake will get smushed - plus if you use the next size board, you'd have to use the next size box.
I use 4" larger boards for bases (especially for wedding cakes), so I'd put a 10" cake on a 14" baseboard.
I use a board 3 inches bigger for smaller cakes, and 4 inches bigger fr the larger ones - 10 inch and over
Here's the way I do it. If I have a three tiered cake 10/8/6 for instance...each tier is on the same size boards 10/8/6..the boards leave about 1/8-1/4 inch "shelf" for your icing and fondant. I never trim my cakeboards to be exactly the same size as my cakes. When you do this your icing and/or fondant don't have anything to rest on. That said....
I make my cake base at least two inches larger than the bottom tier. I usually cover my base cakeboard with a fabric or wrapping paper and clear contact paper (not food safe) so the bottom tier is on it's own cakeboard and not directly on the cakebase. Hope that I'm making sense. If I have a two inch difference in tiers then I'll use a 2" difference for the cake base. If I'm doing a three inch difference 12/9/6 I'll use a 15 or 16 inch cake base.
When I"m just making a cake on a board with a border around the bottom I usually go at least 2" larger than the cake itself.....if the board has a decorative element to it (printed paper, writing, etc.) I go 4" bigger than the cake itself.
For tiered cakes I keep with whatever distance the tiers have between them.
For instance if I do a 6",8",10" cake, I'll put it on a 12" decorative board...I think it's more pleasing to the eye to continue the size difference all the way through to the board, I also repeat any placement of flowers and any ribbons onto the board.