Pearls are measured in millimetres. The figure refers to the diameter in the case of round pearls, or length and width in the case of baroque ones.
What determines size?
The most important factor in determining a pearl's size is the type of mollusc in which it grows. A large pearl for one species may be unusually small for another. Refer to types of cultured pearl for more information.
The other factors which influence size are:
- the size of the nucleus introduced to initiate the pearl. To create a large pearl a larger nucleus must be introduced. There is a risk that the recipient mollusc may reject it and die before a pearl has grown. There is also a greater chance that the resultant pearl will feature large blemishes. Larger pearls are relatively rare especially with fine skin quality, and the risk in growing them makes them more expensive.
- the length of time a pearl is allowed to grow. The more layers of nacre that are deposited the larger the pearl will become.
When choosing pearls for someone, bear in mind their personal style. From a fashion perspective, pearls of over 8 mm are considered fairly dramatic, pearls below 6 mm are considered petite whilst the 6-8mm range is seen as classic.