I have to do a anniversary cake for 100 people. This will be my biggest cake so far. I was going to go with (all 2 layers) bottom 12 inch then 10 then 8 then 6. Will this be enough cake for 100 people. If not any suggestions would be great!

Too much... it will feed 130. Have you seen the Wilton industry standard chart?
http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm

Thank You CWR41. I will check that out.

OK, that chart is awesome. Thanks so much BIG help.

I'd suggest a 6" x 9" x 12" for exactly 100 servings... what do you think?

Thanks that sound great. I didn't have a 10 inch pan so was going to go buy 2. I have the 6, 9 and 12 so that works great. Thanks again. I love being able to get answers to my questions here. Thank you so much for taking the time to help me.