I need to know the size/s to use to do a sheetcake to feed 80. It will be a single layer no filling TIA

If you make a 15x22 full sheet (you can make 2 11x15's side by side), it will make 82 servings that are 2"x2".

With square or rectangle cakes, it's easy to just do the math to figure your servings.....

Single layer:
11x15 cake: 2x2" servings = cut columns/rows of 5x7 = 35 servings
11x15 cake: 2x3" servings = cut columns/rows of 5x5 = 25 servings

12x18 cake: 2x2" servings = cut columns/rows of 6x9 = 54 servings
12x18 cake: 2x3" servings = cut columns/rows of 6x6 = 36 servings

14x22 cake: 2x2" servings = cut columns/rows of 7x11= 77 servings
14x22 cake: 2x3" servings = cut columns/rows of 7x 7 = 49 servings

These are based on a single layer cake. If you bake two layers, then you will probably cut the pieces into 1x2" pieces to yield different serving amounts.

Double layer (pieces are 4 tall same as a wedding cake):
11x15 cake: 1x2 pieces = cut columns/rows of approx 10 x 7 = 70 servings
12x18 cake: 1x2 pieces = cut columns/rows of approx 12x 9 = 108 servings

Just do the math.....!

Thanks