Will a 600cc implant bring me to a DDD in a bra? (Photo)

You may very well be a DDD cup with a 600cc implant. However, among bra manufactures the sizing for a DDD can be different. The best way to detemine the implant size you want would be to do sizing in the doctors office with implant manufacturer sizers. This will give you a very accurate visualization of what you will look like.

a 600cc implant likely will make you larger than a DDD. At your age, you do not have the option to have a silicon implants so you would be getting a saline implants. 600 CC is extremely large particularly for your first breast augmentation. I would suggest a serious conversation with a board certified plastic surgeon before going that large because the rate of complications is significantly higher with very large implants. Best of luck.

Thank you for the question and pictures. Based on your photographs, you are starting at a great place and should have a very nice outcome with breast augmentation surgery.  In regards to specific size/profile of breast implant, despite good intentions, online consultants will not be able to provide you  with  meaningful specific advice.  Ultimately, in person consultation with well experienced board-certified plastic surgeons will be necessary. Careful measurements, dimensional planning, and careful communication will be key.
Generally speaking, the best online advice I can give to ladies who are considering  breast augmentation surgery ( regarding breast implant size/profile selection) is:
1. Concentrate on choosing your plastic surgeon carefully.  Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. Ask to see lots of examples of his/her work.  2.  Again, have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining which operation and/or breast implant size/type/profile will most likely help achieve your goals.
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or "DDD cup" etc means different things to different people and therefore prove unhelpful.
 Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup  size may also be inaccurate.  The use of computer imaging may be very helpful during this communication phase.
3.  Once you feel you have communicated your goals clearly,  allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals.  Again, in my practice, this decision is usually made during surgery.  The use of temporary intraoperative sizers, viewing the patient's breasts in the upright and supine position, are very helpful during the breast implant selection process.
I hope this, and the attached link (dedicated to larger breast augmentation outcomes), helps.