Breast implants used for breast enhancement are not one size fits all, there are many sizes. The saline filled breast implants are designed to be filled to within a recommended volume range. Breast implants are numbered or named by their lowest recommended volume, but most plastic surgeons will fill the breast implant to its highest recommended volume. This not 'overfilling' a breast implant. This is confusing to some woman because they have read elsewhere to be aware of overfilling. Filling a breast implant to the highest recommended volume will usually make the breast implant perform better. It will have a better feel and may be less likely to fail (deflate) than the lower volume filled implant.

A breast implant that is underfilled has been filled to markedly less than the recommended fill range to the breast implant. A breast impant that is overfilled has been filled to markedly more than the recommended fill range for that particular size breast implant. Saline implant problems like deflation, rippling or ball-like feeling can be exacerbated by overfilling or underfilling a breast implant. Examples of marked volumes would be more than 15% more or less than recommended by the manufacturer of the breast implant.

The volume ranges of a breast implant are based on the width of the base of the breast implant. So the wider the breast implant, the more the breast implant can be filled to. This is primarily true for the moderate or medium profile breast implants. The high profile devices have a much greater fill range than the more commonly used moderate profile breast implants. As a high profile breast implant is progressively more filled, it becomes narrower. This is why the higher profile implants can look 'torpedo' like on certain women.