Hii… I need to bake a sheet cake for 30 ppl.. I have got cookie sheet rectangular pan of (300x260x40)MM =( 11.8x10x1.57 )inch. I want to bake a Genoise or Chocolate Butter Cake , however not sure what should be the measurement for batter. I checked TCB for rectangular cake formula could not find any. Anyone has any advice for me ???

sagarika, there are rectangular butter cakes and rectangular genoise included in the wedding cake chapter at the end of the Cake Bible.  Your pan is not a standard U.S. size, but you should be able to come up with an approximate batter amount by comparing its volume to that of the standard US rectangular pans (p. 455). 

Good luck!