Half Sheet = 12x18.
When cut in industry standard 2x2x2" pieces (single layer), the cake will be cut in 6 rows by 9 columns (12 divided by 2", and 18 divided by 2") = 54 servings.Full sheet
= Two of the 12x81's shoved together = 18x24
This cake will be cut in 9 rows by 12 columns = 108 servings.
A 2 layer 12x18 would be cut in 1x2x4" pieces, so the cake would be cut in 12 rows by 9 columns = 108 servings.11x15
For odd size pans I always round down for easy cutting and easy math.
11x15, when cut in 2x2x2" pieces, would be cut in approx 5 rows by 7 columns = 35 servings.
A 2-layer 11x15 would be cut in 1x2x4" pieces, so the cake would be cut in approx 10 rows by 7 columns = 70 servings.
These are the numbers I used to determine pricing. As I've said a number of times, they are welcome to cut the dang cake in half and serve it with two forks, but they are paying for these numbers.