Ok I Have A 1 year old birthday cake to do. The theme is mickey mouse, it's a tiered cake, for 10 guest. The cake that they picked is something Like this https://s-media-cache-ak0.pinimg.com/originals/f3/54/42/f354423a88543ee1c6c54e9d4a1d270f.jpgy

They want something like that but with a small mickey mouse hot air balloon on top. My question is what size pan can I use to make that cake I only on 10inch 9inch and 8inch round pans. Can I do 9 for bottom and 8inch for top? And it's going to be double layer.

Cake Baking and Serving Guide

That's a big cake for 10 people.  Are your clients aware of how much cake that is? Depending on how tall your tiers are, a 9 and 8 will give you approx 50 servings and wouldn't look right anyway. 

The smallest that I would do for a tiered cake is an 8 and 6 and I charge for 36 servings (my tiers are 4 layers and approx 4" tall).  Any smaller than that and it's not worth the work involved to me.

What about doing a single 8" tier with a hot air balloon topper? The topper will give it the height of a tiered cake.  Otherwise, I would by some 6" pans.

Yes they understand it's a lot of cake but they picked a 2 Tiered cake. 

Ok, just checking because most people don't realize how much cake that is and don't want to spend that much money for 10 people.  Sometimes, as the professional, we need to educate our clients and help guide them when they are choosing a design. Most cake designers charge by the serving, so that's always a consideration.

Like I said, a 9 and 8 will not look right-especially if they are shorter layers.  So, you may want to invest in a couple of 6" pans. If you are going to do tiered cakes, you'll get lots of use out of them.

Good luck!