How to gauge flange size when buying a pump online? Does having a big breast mean u need big flanges? Any guideline to follow?

Here's an article provided by a company that manufactures flanges for Medela, speCtra, and Ameda breastpumps. You can have a read to find out more on how to choose the sizes. http://maymom.com/index.php?option=com_content&view=article&id=78&Itemid=484 A lot of my friends had to trial and error. One of them mentioned that if you are using the Medela pump, you can go to their service centre (located at 81 Toh Guan Road East # 03-01 Secom Centre) and they could help you determine the appropriate size.