Pearls are a symbol of fashion and elegance, and many people love pearl jewelry for this reason. Pearls can be very expensive depending on the size and quality. Pearl size is measured in millimeters (mm).  Within the same quality grade, the larger the diameter of the pearl means, the higher the market value. A pearl of the same quality can cost 20% more for every millimeter increase in size. 

The most expensive pearls are the South Sea Pearls. These pearls are the BIGGEST and most luxurious that are produced today. They generally have similar features to Akoya pearls but in much larger sizes. The diameter of a South Sea pearl normally can be above 9 mm, some are 10-15 mm, and the biggest can be 21 mm in diameter. Those that reach 13 mm belong to a rare collection class and are considered high-value pearls.  Big South Sea pearls are usually only made into necklaces because they are large and heavy. 

Different from South Sea pearls, Akoya pearls have the most beautiful pearl halo colors and are small and delicate in size compared to South Sea pearls. Akoya pearls generally range from 5-9 mm in size, smaller and more refined compared to the South Sea pearls, whose average size is 7-9 mm. 

Tahitian pearls are generally between 8 to 14 mm in size, with a small number exceeding 17 mm, and are considered rare treasures. 

There is no limit to the size of Baroque pearls. The largest natural baroque pearl in the world is the Lao Tzu pearl. This natural pearl was discovered on May 7, 1934, in Palawan Bay, Philippines. It is 241 mm long, 139 mm wide and the bead weighed 6.3kg.  

Lao Tzu pearl vs normal pearl ring

So what factors determine the size of a pearl? Today, AngelaQpearl will introduce you to the three main factors that influence the size of pearls:

First, the type of pearl, second, the cultivation method, and third, the cultivation time period. 

The oysters that breed pearls are different, and the sizes of the pearls produced are also different.

Take the Japanese Akoya pearl as an example, its oyster is the smallest among all pearl types, therefore, the Akoya pearl produced is only 5-10 mm. On the other hand, the oyster of the South Sea golden pearl, (also known as the Pinctada Maxima Oyster), is also a sea pearl, however, it can produce large-size golden pearls of over 15 mm!  

Pearl culturing methods and pearl culturing cycles will also play a decisive role in the size of pearls. 

At freshwater pearl farms, each mussel is surgically implanted not with a bead but with 24 to 32 tiny pieces of mantle tissue. Eighty percent of freshwater pearls are made this way. This is called a non-nucleated pearl process. When the mantle tissue has been inserted, a sac forms and cells begin secreting nacre, forming a calcium-carbonate compound - a pearl. One mussel can produce 20-30 pearls. These pearls are smaller than nucleated pearls, and they take longer to grow, 3-5 years or more, depending on the culture period. Non-nucleated pearls produced are small ranging in size from 1 mm to more than 12 mm. 

In the pearl industry, a 10mm non-nucleated pearl is considered large, and growing a freshwater pearl this size takes a long time, generally 5 years. Therefore, growers that produce large non-nucleated pearls invest in the pearls for a long time and must charge accordingly to recover their production cost. This is why large freshwater pearls are considered valuable and are generally high priced. 

South sea golden pearls, South sea white pearls, Tahitian black pearls, and nucleated freshwater pearls, these four types of pearls are often able to grow large size natural pearls because of the nucleated culture method; on the contrary, ordinary freshwater pearls (seedless cultured or mantel implanted) and Akoya pearls are much smaller.

(PS: Akoya pearls are also nucleated, but because the mother shells  are very small,  Akoya pearls are small, too.) 

The size of the pearls will vary depending on the breeding cycle: the longer the breeding time, the more nacre layers secreted by the mother-of-pearl oyster, and the larger the pearls will be. 

For both nucleated sea water pearls and nucleated freshwater pearls, the nacre must be thick enough to maintain the luster of the pearl. For example, South Sea pearls must ensure that the pearl oysters grow on the bottom of the sea for at least six years, and have a pearl layer that  is thicker than 0.3mm, to ensure that the surface of the pearl is smooth and free of any impurities. 

It is worth noting that the popularity of Akoya pearls in recent years has led to a large number of low-quality Akoya pearls in the market. The breeding cycle of these low quality pearls is only 8 months, resulting in a pearl layer of only about 0.1-0.2mm. If you want to buy Akoya pearls, it is best to choose a pearl layer above 0.4mm. Poor quality Akoya pearls with only a few months cultivation will peel off easily or will lose their luster in a short period of time. 

Your AngelaQ free guide to different pearl sizes and different pearl types: 

South Sea white pearls: 10-15mm+, South Sea golden pearls: 9-15mm+, nucleated freshwater pearls 9-15mm+, Tahitian black pearls: 8-15mm, Akoya pearls: 3.5-10mm, Non-nucleated freshwater pearls: 1-12mm.