The most commonly used and internationally recognized ranking system consists of B, A, A+, AA, AA+, and AAA to grade the pearls. On this scale, AAA is gem-quality, and the absolute highest quality pearl available. Six accepted factors determine the quality, value, and beauty of pearls. They are nacre, luster, surface, shape, color and size. These six factors are universally accepted as the main factors in grading a pearl.

Nacre is the natural substance that a mollusk like a mussel or oyster secretes to protect its sensitive flesh from irritants such as sand, shell fragments or implanted beads. This nacre is the same iridescent material that lines the inner surface of the oyster shells, aptly named mother-of-pearl. As a general rule, the thicker the nacre, the higher quality the pearl is.

Luster is quality of a pearl that shows its mirror-like reflecting ability and surface brilliance, it's glow. The luster of good quality pearls should be bright. Found on the very surface, luster is measured by the sharpness and brilliance of the reflection. A good quality pearl captures light well and reflects it back to the observer's in an impactful manner. You'll be able to see your reflection clearly on the surface of a good pearl. Pearls appearing too white, dull or chalky are not of high quality.

Grades of pearl luster are: Very High (AAA), High (AA & AA+), Medium (A & A+) and Soft (B). When reflections are bright and sharp, pearls are said to have high, or very high, luster. When the light reflections are weak or fuzzy, pearls are described as soft or dull. High luster pearls are obviously coveted as the luster plays a singnificant role in the beauty of a pearl. High luster can make up for sub-par size, shape, color and surface.

A pearl's surface is probably the most obvious and easiest to observe. The cleaner the surface of the pearl, the more valuable it is. Look for an absence of disfiguring spots, bumps, cracks, discolored portions, areas of low or uneven nacre appearance, or any other flaw on the surface of a pearl, also known as "cleanliness." Notice that the highest quality pearls have a sharp, mirror-like reflection. The ideal good quality pearl is one that is free of imperfections.

The surface quality of a cultured pearl is rated as follows: Clean-Very Lightly Blemished (A quality), Lightly Blemished (B quality), Moderately Blemished (C quality), Heavily Blemished (D quality). All surface grading is done with the naked eye (no magnification device like a jeweler's loop) and is very subjective, depending greatly on the expertise of the grader.

Pearls develop in all shapes, especially freshwater and Tahitian pearls. They can be round, semi-round, drop, oval, half-rounded, semi-baroque and baroque baroque shapes. The general rule of thumb is, the rounder a pearl is, the better the quality, assuming all other factors are the same. A perfectly round pearl is very rare. Other shapes that are not symmetrical in shape, can be lustrous and appealing, and typically cost less than round pearls.

To be considered round a pearl must have an almost perfect spheres whose diameter variation rate is less than 2%. A semi-round pearl has slightly imperfect spheres whose diameter variation rate is greater than a round's 2%, but less than 5%. A semi-baroque pearl exhibits at least one axis of rotation (it can be spun on a table top) and are subdivided into four shapes: drop, button, pear and oval. A baroque pearl does not have any axis of rotation at all (cannot be spun on a table top).

Pearls come in a variety of colors, from white to black and every shade in between. The color of a pearl is a combination of two components; its predominant basic body color and its overtone, and it is important to distinguish between the two. The body color of a white pearl may appear in white, pink, cream, champagne, aqua, golden, green or black. An overtone is the color that overlies the body color resulting from the layers of the nacre, and may be seen under different angles of the light.

Typical overtones are rose, pink or silver. Every pearl developed appears with a different color combination, which makes it truly unique from other pearls. Color itself is not the basis in grading pearls rather it is color intensity. A good quality pearl possesses a deep and equal overtone while a bad one possesses the opposite.

Measuring the size basically means measuring the diameter of the pearl expressed in millimeters. Tiny seed pearls can be smaller than 1 mm, while South Sea pearls as large as 20 mm have been found. If all other quality factors are equal, the value of the pearl rises gradually with size. Round and off round pearls are measured by the shortest diameter. All pearls in other shapes are measured along two diameters (the longest and second longest). It is important to remember, that size alone however is not enough to tell the quality of the pearl.