Non-graduated pearl necklaces are strands of matched pearls that feature matched pearls that progress no more than 1.0 mm in size from smallest to largest. These necklaces can be very difficult to match, and may take years to complete as the person creating the layout must wait for very specific pearls matching in size, color, overtone, luster and surface quality This makes non-graduated strands more expensive than non-graduated necklaces. Non-graduated necklace measurements will appear as so: 10.0-11.0 mm or 9.9-10.9 mm and so on. The necklace only qualifies as non-graduated if the pearls range in size less than 1.0 mm.
Graduated Tahitian pearl necklaces have a wider range in size, and most often includes pearls that graduate from 2.0 to 4.0 mm. So a typical graduated necklace would have measurements like this: 10.5-11.9 mm or 9.8 to 12.25 mm and so on. These necklaces are much less expensive than their non-graduated counterparts as the sorters creating the necklace layout have a little bit more wiggle room in terms of pearls to choose from that will fit with the necklace's overall tone, color, size and shape.