After I got the first couple of mails regarding princess seams, I decided to post a tutorial here. But then again, I got yet another request from a dear reader on the same, and so I thought to make a 'clearer princess seam post'
The labels 'A', 'E' and 'B' stand for the Apex(nipple or highest point of the bust), Empire (that area under the bust, normally measured from the top of the shoulder to the underbust i.e. where your bra rests), and Bodice (your belly button, normally measured from your shoulder to belly button)
The determined width would read as technical if I explain it, so I would just advice that you add about 12'' to half your bust line measurement and if you are making a dress, add to your hip measurement. If you are bigger however, feel free to add incremental inches so you don't make errors and waste your fabric.
Fold your fabric in two: measurements used here - bust(34), bodice(17 x 26), empire(27)