I haven't been on here in so long, and my cousin was needing to know what a sheet cake serves and I have forgotten, I actually stopped doing cakes, so I didn;t know what to tell her!

here is the wilton serving chart there are different sizes of "sheet" cakes as well as depth
http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm

If it's 2" high, then you cut 2" x 2" servings. So it depends on what size your sheet cake is. A 12 x 8 would serve 24.

Thanks, I guess it would be important to say it's a FULL sheet she is wanting!!

The good news on rectangle cakes is that it's easy to do the math to figure your servings, as explained in this thread: http://forum.cakecentral.com/cake-decorating-ftopict-653932-math.html