What is a carat? Carat Weight and Millimeter Dimensions of a Gemstone Explained

We get quite a few inquiries from customers asking why the same millimeter size of gemstone has different carat weights from one gemstone to another. We also get customers saying he/she expected the gemstone to be larger/smaller because of the carat weight listed. We thought we should take a few minutes to explain why this is.

Aquamarine Gemstone Earrings - Peora JewelryCarat is a unit of measurement. It is used to measure mass or weight. You might think of diamonds when you hear the word “carat,” but it is actually used to measure all types of gemstones in jewelry.

A carat is exactly 200 milligrams or 0.2 grams. When referring to diamonds, most jewelers will use the term “point” or “pointer” to describe the size of a specimen. As you may have guessed, a “point” is 0.01 carat or 1/100th of a carat. So a ten “pointer” diamond would be 1/10th of a carat or 0.1 carat.

Now, when we try to equate carat weight to physical dimensions like millimeters, things get a bit tricky. Because diamonds and gemstones come in all sorts of shapes, each shape will convert differently between carats and millimeter size. With diamonds, it is generally accepted that a 1.00 carat round diamond will be 6.5 mm in diameter, but a 1.00 carat princess or square shape diamond will be 5.5 mm in diameter.

Emerald Gemstone Pendant Necklace - Peora JewelryDiamonds are more or less the standard comparison for carat weight and millimeter size. However, depending on the type of gemstone, the carats to millimeter difference can vary widely. Each gemstone or mineral type has a different density, which means it will convert from carats to millimeters differently.

Let’s take the diamond’s most commonly used inexpensive stand-in, Cubic Zirconia, as an example. The Cubic Zirconia is actually much denser than diamond, roughly 1.7 times as dense. So a 1.00 carat round CZ would actually be only a 5.3 mm diameter compared to the 6.5 mm of a diamond with the same carat weight. Some other gemstones that are more dense than diamonds include: sapphire, ruby, alexandrite and garnet.

Garnet Gemstone Ring - Peora JewelryConversely, let’s take Opal as another example. Opal is significantly less dense than diamond so it will be a much larger size stone with the same carat weight. A 1.00 carat round Opal will be almost 8 mm in diameter compared to the 6.5 mm 1.00 carat diamond. Other gemstones that are less dense than diamonds include: amethyst, tourmaline, aquamarine, emerald and quartz. Topaz and Peridot are fairly close in density to diamond.

So what do we take away from all of this? Basically, if you are searching online for a piece of gemstone jewelry that is not a diamond, you might as well disregard the carat weight altogether. Just look for the millimeter dimensions of the gem and pull out your trusty ruler.

New Line of 14Kt White Gold Tanzanite and Diamond Rings

We’ve been working on this project for what seems like the whole year and finally it is live! A beautiful new line of solid (and rather hefty) 14Kt White Gold Tanzanite and Diamond Rings. The main reason it took so long to get this project finished was trying to find the perfect Tanzanite gemstones to fit the ring mountings. It took some time but was well worth it in the end. All of these Tanzanite are just gorgeous with a super rich purply-blue hue and great sparkle, and each one is just a little different in color to make each one unique.

We also finished a line of IGI Certified 14Kt White Gold Solitaire Diamond Rings in several diamond sizes. To go with the Solitaire Rings, we also added a few pairs of White Gold Diamond Stud Earrings in a few diamond sizes.

In other news, the new Halo Gemstone Sterling Silver Rings previously mentioned here have arrived and are off to the photographer along with a few Opal Sterling Silver stud earrings and an awesome new line of White Gold Double Sided Checkerboard Gemstone Frame-less and Framed Fishhook earrings. We are super excited for the new gems to come and should be available soon. Keep your eyes peeled.

Here are a few of the new Rings and Earrings:

3.26 cts Pear Shape Tanzanite Diamond Ring in 14Kt White Gold Size 7 R61926 5.30 cts Trillion Cut Tanzanite Diamond Ring in 14Kt White Gold Size 7 R61960 6.57 cts Oval Shape Tanzanite Diamond Ring in 14Kt White Gold Size 6.5 R6196214Kt White Gold Diamond Earrings 14Kt White Gold Diamond Solitaire Size 6 Ring, IGI Certified

New Designs Added – Silver Pearl Rings, White Gold Gemstone and Diamond Pendants and Earrings

We have just added a bunch of new items:

Sterling Silver Freshwater Pearl Rings Peora Jewelry

A set of Sterling Silver Freshwater Pearl Rings. We have quite a few more Pearl designs in the works – Pendants, Earrings and more Rings in about a month.






New Sterling Silver Emerald, Citrine, Alexandrite Gemstone Bracelets Peora Jewelry

We have re-made a few of our best selling Gemstone Bracelets now in Lab Emerald, Citrine and Lab Alexandrite.








A huge batch of simple 14k White Gold Gemstone and Diamond Pendants and Stud Earrings.

Come check out the great new stuff at Peora.com!