I've found a few tables here for how big cake for x number of people, but dont know if what is given is considered layered?

I need a round cake for 25-30 people. I'm thinking either a 10" round cake (2 layers) or should I add an 8" cake on top (2 layers) Or a 8 and 6-inch cake? There's gotta be a magic table somewhere?

http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm

I would say a 10 inch would be fine. Probably a little more cake then you need or you can do an 8 and 6 for a 2 tiered look. Either way you will have a little more cake then you need.

thanks!

6" serves 12
8" serves 24
10" serves 38
12" serves 56

From the wilton wedding cake serving chart. based on 1x2x4" industry standard pieces.

See link in my signature on how to cut a cake to achieve these serving sizes.

that's because I dont' own or use odd size pans (no 9's, 11's, etc.)

Yeah, me neither, but 9" is included on the Wilton chart.