Going from 300 filled to 330 to 210 filled to 230-240 saline implants. Will there be a significant change in size?

The difference relatively speaking will be affected by the size of your breasts excluding the implants.  If you have no breast tissue then you will loose a third of your breast volume when your implant is removed.  If the implants only make up half your current breast volume it will only be a 15% change.Dr Rodger ShorttPlastic SurgeonMD, FRCS(C)Ass't Clinical ProfessorDirector of Cosmetic Surgery Training,McMaster University

The size difference depends not just on the size of the new implants but also the amount of breast tissue you currently have.  A very small person might notice a significant decrease in size but a larger-breasted person might not, if they already have a lot of their own breast tissue.

It appears you have implants larger then you or your surgeon anticipated. This reduction in size will be 1/2 to 1 cup size depending on the type of bra you wear. 175cc may be a size that you and the plastic surgeon might consider. Shaped implants may be a better option. Be clear about your objectives with your plastic surgeon. Good luck...

It is very difficult to determine the exact size and shape implant you will require to best match your ideal breast image without an examination by a board certified plastic surgeon. The 100 cc size difference is between 3-4 shot glasses in volume. Choose not just any board certified plastic surgeon, but one with many years of frequently performing breast augmentation surgery including different approaches, techniques and implant choices. This is because several measurements not to mention your breast characteristics are needed to determine the optimal implant size to obtain your goals. Without knowing these dimensions it would be difficult to make this determination. For example, the existing base width of your breast will determine, in many cases, the maximal volume per implant profile that you can accommodate. To illustrate; a 100 cc difference may make a significant difference with a narrow base width breast, but much less of a difference if you have a wide chest wall and wide breast “foot print”. Therefore, just because your friend may have a great result with let’s say a 350 cc implant to make her go from a “A” cup to a “C” cup size does not mean that you will have the same result with the same size implant. . Further simply placing implants in a bra to determine the size best for you is not always accurate as the bra often distorts the size, is dependent on the pressure the bra places plus the implant is outside your breast and not under it among other variables. Computer software morphing programs that automatically determine the best implant size can be helpful in some but not all cases (e.g. doesn’t work well in my experience with existing implants, sagging or asymmetric breasts). Using “want to be” photos however are useful if simply provided to the surgeon as I will further explain in the below link.

madig, Generally a 75-100 cc change is necessary in order to perceive a significant overall volume change, whether going larger or smaller. Too small and the tissues will not fill out adequately, so this sounds right, but photos are much more helpful in assessing such geometric/size issues. There is no formula for choosing implant
size and geometry, as a lot has to do with the existing breast volume, breast
base dimensions, location of your breasts on the chest wall, and then your
personal desires. This includes how natural versus how
obviously augmented you wish to appear. You will find that there is
a range of effective volumes for each patient, below which the breast will not
be adequately filled and will not reach its best shape potential (least
effective volume), and beyond which the breasts will give up natural shape for
the sake of additional outcome volume (maximum effective volume). Additional
volume can be added beyond the maximal effective volume, but will transform the
shape to a less natural-appearing roundness and then on to a completely fake-looking
shape, eventually reaching a point where the addition of further volume
requires destruction of internal muscle and fibrous support structures, and
breach of breast landmarks (mainly the folds), which in some patients will lead
to double fold contour deformity, bottoming-out, symmastia etc. Implant
Sizing schemes with, external implants in a bra, may be of some help, but
can be misleading if an implant volume and width is desired that is beyond
the capacity of the breast fold geometry, particularly if there is mild skin
overhang over the lower pole fold (dedicated fold geometry). I find
that bringing photos of similar shaped women's results can help in the
discussion, but realize that photos can only be used as a theme for what
you are looking for, and not like a catalog from which exact sizes
and geometries can be ordered. I hope that this helps. I hope that this helps.     A patient with a similar circumstance to yours if shown on the page linked below.