Is a 650cc breast implant a good size if I want to go bigger from a 34d?

Thank you for the question.  Online consultants will not be able to provide you with specific enough advice to be truly helpful. Ultimately, careful communication of your goals (in my practice I prefer the use of goal pictures, direct examination/communication in front of a full-length mirror, and computer imaging) will be critical.
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. Have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining 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. For example, I have found that the use of words such as “natural” or "D or DD cup” or "busty" etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on him who makes the bra; therefore, discussing desired cup size may also be inaccurate. Again, the use of computer imaging has been very helpful during the communication process, in our practice.
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, after the use of temporary intraoperative sizers.
I hope this (and the attached link, dedicated to breast augmentation surgery concerns) helps. Best wishes for an outcome that you will be very pleased with.

There is no way to guarantee a particular bra size. Bra sizing varies greatly between bra manufacturers and a C in one bra will be a D in another. What matters more than the assigned bra size is the way the implant looks on you. The best option for your body and aesthetic goals can be determined in a thorough implant sizing session.Implant sizing depends on several factors. One of the most important factors is your breast width. Generally, your surgeon will measure your breast width, and then provide you with a range of implant sizes appropriate for your native breast size. There are more nuances to it than just what I've described, but this approach works for most women.I usually have my patients bring in a large bra and a tight t-shirt to do sizing. I'll then choose 3-4 implants that I feel are appropriate, and have my patients place them in the bra under the tight t-shirt. My patients can then look in the mirror and get a good sense of what they will look like with the provided implant sizes. My patients like this approach and get a great idea of how they will look.By using this technique, your surgeon can outline a range of appropriate implant sizes that will be aesthetically pleasing, and you make the final decision.I hope this helps. Good luck!