Column Calculation

Hi, I have this table:
Column Name      Data Type        
BookNo                           Number(10)        
CustNo                           Varchar2(6)
RoomNo                           Number(3)
InvoiceNo                           Varchar2(10)
BookDate                           Date
NoG                           Number(3)
CiD                           Date
CoD                           Date
LoS                           Number(3)
CCNo                           Char(12)
CCType                           Varchar2(6)
CCExpiryDate      Date
Status                           Varchar2(10)

e.g. Number(3)   = (3/2)+1 = 3
       Varchar(10) = 10+1   =11
       Char(2)         = 2+1     =3
       Date              = 7+1     = 8
       Total                            =24

        #Total column size = 24+1=25 (this is just an example)
 
A. Does my calculation method for each different data type correct? Why we have to add 1 and why for Date datatype we calculate as 7?

B. And say if the total column size above = 200 and the row header size is 3, then how to calculate the row size? Is it 3+200+13(total column in booking table)?

Thank you b4 for anyone who helps me.