Welcome to the mm (millimeter) to Carat Weight Conversion Chart, or Carat Weight to MM, it’s all the same. :)
Why do we need to figure out a Diamond’s mm size and convert it to Carat Weights?
Because it helps us make some very important decisions when it comes to Diamonds and Diamond Rings…
- You can use the measurements to figure out what the approximate Weight of a stone is.
- You can figure out what mm size head you’ll need in order to set a Diamond into a ring or mounting.
- You’ll be able to tell if the stone is cut properly or if it’s too wide or too deep.
- It can help you identify your stone, by comparing it to the measurements on your Certification Report. Which will also help you tell if your Diamond was switched or not!
As you can see, there are a lot of great reasons why one would want to compare and convert millimeters to Carat Weights.
Diamonds and Gemstones are Cut Differently for a variety of reasons:
- To preserve Carat Weight.
- To utilize the Parent Rock.
- To enhance a Gemstone’s Color (deeper Gems give darker color).
- To remove flaws or blemishes from the stone.
Gems are like people and will vary greatly, but one thing’s for sure, the mm sizes of them will almost never be exact. They can be close, but they will always differ depending on how they are measured and the instruments used.
As a Test…
As a test, try to find a Diamond with an exact mm width of 6.5 mm in a Jewelry Store. Not easy eh? In fact, I would probably bet that you couldn’t find an exact measurement. Close, but not perfect. Nothing that man is involved in is ever perfect. Especially when it comes to Diamonds and Cut.
That’s why mm is used to arrive at an approximate Carat Weight. Approximate Weights are needed when a Jeweler is trying to judge the Carat Weight of a Mounted Diamond. These mm Measurements are listed on a Diamond Certificate as shown below…
Certified Round Diamonds are generally measured in 2 different spots from one side of the Girdle to the other (just to make sure the Diamond is really round). Normally a Jeweler would average these mm widths together to arrive at one mm measurement.
Stones like the Oval Cut or Marquise Cut are measured across the stone and up and down as in the images below…
Diamonds like the Tapered Baguette Cut are measured at both ends of the Diamond and the length of the stone as well.
Let’s look at the mm of a One Carat Diamond for another example.
One Carat Diamond mm Size
A One Carat Diamond (1.00) has an estimated mm width of 6.5 mm.
This width is the classic and ideal measurement for a stone that size. Sadly, not all One Carats are cut this way. Most are not! Diamonds are cut deep or wide to maximize profit and the parent rock. This variation of the cut will make a Diamond either look smaller than it really is, or larger. All this has to do with how wide the Diamond appears.
If a One Carat Diamond has a width of 6.0 mm, then that Diamond will actually look more like a 3/4 Carat Diamond (75 points) instead.
So you may be paying a large ticket price for a big stone, but that stone could look quite small in comparison.
Check the Diamond’s measurements and see for yourself.
Your stone could be a VS1 Clarity, F Color, but if it’s cut too deep or too wide, it will lose light, life, sparkle and fire. :(
The mm to Carat Weight charts shown below are only the measurements of a face up Diamond (the width of the outline or shape of the stone).
The depth of the stone is not given in these approximate Carat Weights. It’s assumed that the depth is a good cut. To get the true weight, you’ll also need to calculate in the depth of the stone. But that can be deceiving since the Diamond could have a thick Girdle or heavy Crown. Plus, when it’s set in a head, you can’t truly get to the Pavilion to measure the stone anyway. It makes it an impossible task. Estimates are given, but that’s all they are…
To get an exact weight, you’ll need to remove that Diamond from the mounting and have it weighed on a Diamond Carat Scale (Modern Scales are Digital).
That’s the best way to, well, weigh! :)
Until then, approximate weights are used.
The most common Cuts of Diamond are shown in the Guides below: Round, Princess, Marquise, Heart, Oval, Pear, Trillion, Emerald, Radiant, Cushion, Baguette (Straight and Tapered).
So look at your Certificate for the mm size, or get out your mm Gauge, because Carat Weights and mm sizes are up next…
Diamond MM to Carat Weight Conversion Charts