Thank you for your question. This is the most important consideration when planning your surgery. The fist thing to note is that, as you probably know, cup sizes are very variable between shops and bra styles / brands. For example, one could fit into a 'B' cup bra in M&S but in another store, one would fit a 'C' cup. Overall, it is more important to aim for a look rather than a specific cup size. The second aspect to note is that an augmentation must be based around your current anatomy and measurements for it to look appropriate and for safe outcome. During your consultation, your surgeon should take measurements of your existing breast tissue and then help you decide the appropriate size based on your anatomy and on your aesthetic goals. One way to do this is using a sizing kit, which gives you an idea of how you might look after an augmentation using different implant sizes. The third piece of advice is that is always best to see someone who specialises in cosmetic breast surgery, as they will have a full understanding of your options. I hope this helps.