I'm 5'4", 142lbs and aiming for a full C cup. Should I choose 405cc or 450cc?

Patients often think in terms of cup size when considering augmentation. Unfortunately, devices are sized in terms of milliliters (cc) of volume. This can lead to some confusion when sizing. Additionally, it is important to remember that cup size itself is not standardized with variations from one manufacturer to another. Unfortunately, as many women can attest their cup size in an industry leader such as VS is not necessarily transferable to another brand.
Another point which is often under appreciated is that of anatomy and starting point. Any implant will add volume to the volume which is already present. The implant is additive. A particular volume will not necessarily confer the same cup size to different patients (often times it will not even confer the same cup size to different breasts in the same individual...remember they are "sisters" not "twins"). 
A general rule of thumb is that 125cc can represent somewhere between 1/2 to a full cup size increase. Smaller volume differentials (25-50cc) are typically less consequential representing a volume change of less than a shot glass. However, I have found these numbers, at least anecdotally, to be of little help. Patients often present with notions/goals which do not correlate with these sorts of sterile volumetric assessments.
When sizing patients, there are a number of useful tools including:
-3D imaging (has the added benefit of offering a volumetric analysis of the pre-operative breast)
-Breast sizers (rice bags)
-Goal photos
I also recommend that patients commit to a particular look rather than a cup size. Once a patient settles on a look that pleases them the overall cup size increase becomes less relevant.The key to obtaining a natural result is to stay within the parameters defined by your BWD. This will ensure that you avoid the dreaded "fake" look. 
I would not struggle over 45 cc as this will make a very subtle difference in final outcome (approximately equivalent to a shot glass). The best advice is to love the look not the cup.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

Dear Ree,         Front and side view pictures of your breasts would have been very helpful. If indeed you are currently 36 A cup size, to become 36 full C cup size, you will need implants with volume of 450 cc.  However, I have been in practice for over 30 years and performed breasts augmentation on thousands of patients. I have noticed that women tend to over estimate their breasts' size, mainly, because bra manufacturers like Victoria secrets make the cup size small , to let  women feel better about their breasts size.    So, if on measurement (by your surgeon) you are in reality 36 small A cup size, you will need implants with volume of 525 cc to become 36 full C.   You have to realize that not all results are the same, because experience, technical skills and aesthetic eye are critical for good outcome. So, do your due diligence carefully and choose your surgeon wisely.    Always, consult with experienced board certified plastic surgeons who operate in accredited surgery center for your safety. Most importantly, check the before and after pictures in the photo gallery, to make sure that they are numerous, consistent and attractive with nice cleavage, perky, symmetrical and natural looking.                Best of luck,                                   Dr Widder

Hello and thank you for your question.  The
best advice you can receive is from an in-person consultation.  The size, profile, and shape of the
implant is based on your desired breast size/shape, your chest wall
measurements, and soft tissue quality.  This decision should
be based on a detailed discussion with equal input from both you
and your surgeon.   Make sure you specifically look
at before and after pictures of real patients who have had this surgery
performed by your surgeon and evaluate their results.   The most
important aspect is to find a surgeon you are comfortable with. I recommend
that you seek consultation with a qualified board-certified plastic surgeon who
can evaluate you in person.
Best wishes and good luck.
Richard G. Reish, M.D.  FACS
Harvard-trained plastic surgeon