In order to find the right implant size, I highly recommend consulting with a surgeon who allows you to try on implants at the time of your consultation.  This will give you the opportunity to try on actual implants so that you can see if a certain size gives you the result you are looking for.

Size is usually based on breast characteristics such as your personal goals and what you have pictured in your mind’s eye, as well as physical characteristics such as breast tissue elasticity, nipple location, current amount of breast tissue available, and the width of your breast.

You’d also want to keep in mind variables such as where you want your incisions, and whether or not the implant’s placement is well hidden beneath the breast.  As every body type is different, your unique anatomy would also play a role in size selection and choosing an option that ‘fits’ your body well.  I’d schedule a consultation and thoroughly discuss all possible options with your board certified plastic surgeon, before making any concrete decisions.