Hi, I'am doing a coffin cake and the customer wants it to serve 50ppl. So i have a 12x18 sheet cake and after i cut the shape it comes out to be 8x15. So my question is would an 8x15 3 layer cake serve 50ppl??

in theory yes it should a 1x2x3 layer cack should be plenty 60 servings

but it would depend on who cuts it. at a party people tend to cut much larger slices like 1 1/2 x4 so if she serves it herself yes if not then she better have other food available. as people will cut huge slices.

Thank you so much!! I will let them know.

Do the math: 8x15x6", when cut into 1x2x6 pieces means the cake will be cut in 8 rows by approx 7 columns = 56 pieces.

You have room to spare.