Hello!

I need to bake a sheet cake for 60 people/servings.

I have a 12x18 sheet cake pan- would that suffice?

If not, what size sheet cake do I need to make for 60 servings?

A standard piece of cake is 1x2x4 inches.  If you stack the sheets to 4" multiply 12 x 9 and you get 108 pieces.  If the cake is only 2" tall multiply 6 x 9 and get 72 pieces.