BWD measurements are not an "absolute;" each surgeon may measure differently.
Since the breast base does not have a "sharp" beginning and ending point, each surgeon has his or her own way of determining the measurement, but typically does those measurements the same way for each of his or her patients. Decision are made accordingly. If each surgeon has a different end-decision (recommendation for you), then I understand the question and concern.
You didn't include your height or weight, but you look petite, and your measurements are a less-critical starting point than your own request for final size. You look to be an A-cup in size (maybe a B-cup at Victoria's Secret), and I believe it takes about 250cc to go up one cup size. So if you want to be a big B or small C-cup in size, use the 250cc implants, and choose the profile based on the submuscular pocket base width, which will be determined in the operating room, but can be "estimated" by the pre-operative BWD measurement.
If you want "a full C" as you have stated, you should go with the 375cc implants in the proper profile to fit your base width--that implant volume will be closer to your goals, IMHO.
Read my article (on my "About" page) titled: "What is the Right Breast Implant Size for You?" or read the link below for more information. Best Wishes! Dr. Tholen
Breast width measurements
There are many conflicts if what you heard was accurate. There shouldn't be a 2 cm difference from one surgeon to the next, plus a Mentor 225-250 implant isn't wide enough if you truly are 13 cm wide. Sounds like you need another opinion from a very experienced plastic surgeon. Also, the 225-250 ccs would never get you even close to the look you want or the cup size either.
This is exactly why going off measurements isn't as critical as the skill of the surgeon putting the implants in. An experienced plastic surgeon will know which profile will fit for you taking into consideration what type of look you are going for.
Your breast width diameter is what it is. If measured with a caliper, there should not be a variance among different plastic surgeons. I agree that in your case a third opinion would seem advisable. Good luck!
Is it Normal for BWD measurements to vary from surgeon to surgeon?
There are a few options you can consider. But the final decision is yours. Go seek a third boarded PS opinion. Return to each of the previous 2 doctors to discuss these concerns in further detail. From your description and posted photo, " I don't want to look "fake", but I do want to achieve a full c cup.", this might not be possible to "your" happiness. I think the larger cc's amount would be a better option. Remember measurements can vary but the artist experienced eye of the surgeon is more important.
Conflicting BWD Measurements
The BWD is not an exact measurement, and I would accept a difference of a centimeter or so between the 2 docs..
Choosing the proper profile and size of an implant is important in getting you the best result, but this is generally the problem of the surgeon. You should choose your surgeon based on how well you feel the two of you have communicated your desired results, and how well they have responded to your questions and concerns.