Agreed, For SQL Server a general rule that I use anything less than 10 characters should be char. Of course it always "Depends"

when calculating size of a row.

Maximum size of all variable-length columns = Max_Var_Size

Total size of variable-length columns (Variable_Data_Size) = 2 + (Num_Variable_Cols x 2) + Max_Var_Size

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/createdb/cm_8_des_02_92k3.asp