About shirring

[michilaine.livejournal.com]

Hello everyone!
I searched through the memories many times befor deciding to post this question, but found nothing that could help me.
I have always wondered how many cm a shirring panel can add to a dresses actual measurements. I am a big girl and struggle quite much to find fitting clothes. Every time I search at hello lace, lolibrary, most brand sites and mbok or Y! Japan I find that the sizing listed is usually NOT the maximum the garment can give. I know a dress/jsk/skirt can have: 1/4, 1/2, full back and full shirring. But I have no clue how much cm/inches each of these will give me! It happens to me all the time that I find a wonderfull dress on a japanese auction site and see on the photos there is shirring, but sadly I cannot know how much thsese shirring panels will add to the piece.
Any hep here? Suggestions, expiriences with different tipes and sizes of shirring?
Thank you so much for your help!