These are Wilton guidelines for the amount of batter to use in various sizes of round cake pans:

6" pan - 2 c. batter
8" pan - 3 c. batter
10" pan - 6 c. batter
12" pan - 7 1/2 c. batter
14" pan - 10 c. batter
16" pan - 15 c. batter

As a general rule of thumb, pans should be filled between 1/2 and 2/3 full, depending on your recipe and how much it raises. I would suggest making a "test run" with your recipe before you begin a big project.