material master

hi all

i have a query. in my material master basic data 1, i maintained the base unit of measure as KG, and gross weight is 12kg and net weight is also 12kg.

my sales unit is case and coversion is 1 case eqals to 12 kg.

when i am creating sales order for 1 quantity, the gross weight is coming to 144kg. infact it should be 12kg only. how it is happening. can any one please suggest me the best practice.

regards

rag