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How to Choose a Diamond Size & Shape Like A PRO!

Does size matter? Why is the size of the diamond so important?

Well, first it contributes to its rarity which directly affects the price & the value. Why else? Because Size is something that you see, you don’t need a loupe or any fancy equipment, it is something you definitely notice, something that can be measured and weighed. However, size and shape preferences are very personal and should be addressed when you are shopping for a diamond.

Watch the video below which will reveal the secret tips and tricks about getting the best diamond size at the best value for you and what sizes and shapes matter most in the trade.

And, of course, if you need expert help, I am here for you! Just email me or book a consultation & I would be happy to advise you :)


The modern carat system started with the carob seed. Early gem traders used the small, uniform seeds as counterweights in their balance scales. The carat is the same gram weight in every corner of the world, so it was something that was universally understood. The abbreviation for carat weight is ct. Don’t get it confused with Karat with a K is for metal fineness, like 14kt.

One carat of diamond is equal to 100 points. Anything less than 1.00ct is referred to in points, like .25 ct is 25 points or you can say a quarter carat. How do we get the precise carat weight. To get the precise weight of a diamond it is placed on an electronic scale that goes to the thousandths decimal, if the last number is a 9, you round up. The carat weight is always expressed to the hundredth, so 1.039ct= 1.04ct.

If you have a mounted stone, the weight is always approximate and is calculated in so far as the mounting allows. In some mountings you cannot get the exact measurement. For this, you use what is called a leverage gauge and measure in mm. For a round shape, you measure its diameter in up to 4 spots and depth and fancy shapes have a length, width and depth. Each diamond is calculated using the appropriate formula depending on the shape. For both rounds and fancies there are adjustments that are made for girdle thickness and any kind of bulging. The easiest way to calculate the approximate weight is to find an online gemstone calculator like omni calculator that you can plug the numbers into & it will calculate the estimated weight for you.

There are estimated mm charts that just take into consideration the diameter or length x width—this assumes that the depth is “ideal” which isn’t always the case. You can have a 6.5 mm round which is ideal for a 1.00ct, but if your depth is too shallow or too deep it may actually weigh less or more. So that depth measurement—from top to bottom is an important factor especially when calculating larger stones because each point matters when determining the value.

Why a lab certificate? An independant laboratory, like GIA, has all off the instruments to give exact measurements and angles.

So why is it so important to get the exact weight of the diamond? In the diamond world, there are what is called “magic weights”. And to get the list price of a diamond every jewelry/ appraiser uses The diamond trade pricing guide. The list prices are separated by weight category, then color & clarity like a chart. The magic numbers are 0.50, 0.70,0.90,1.00, 1.50,2,3,4,5,10. So once you hit the weight of the magic number, then the price per carat increases. The increase is not linear, it changes depending on color, clarity, popularity, supply. There used to be a trick to buy slightly under the magic weight, so people would get a .97 ct which can look exactly like the 1.00ct. But those stones that were slightly less than the magic weight became higher in demand, so the price break isn’t as much as it used to be. But if budget is tight, I would recommend going slightly under the magic number and if the mm size is similar.

But Be careful, you don’t want to take this “magic number” hack too far. Using the 1.00 ct as an example with a 6.5 mm diameter. You do not want to deviate too much from that ideal mm measurement. For a stone that weighs a lot less, but has the same mm measurement, then the depth is too shallow. Who cares, it looks big from the top. Well, because of diamonds optics, it creates what is called a fish eye. A fish eye is actually the reflection of the girdle inside your stone, so it will look watery if you have a facetted girdle. If you have a frosted or unpolished girdle, the look will be very unpleasing.

Now if someone is offering you a deal for something that weighs a lot more than 1.00 ct but again has the same mm measurement, then it is too deep. Having something that weighs more, but size-wise looks the same is not only a waste, but it compromises the look and the value. A deep stone is called a nailhead. And again, due to optics will make the center of your stone look very dark No matter what color the diamond is. And if it is deep due to a very thick girdle, then it will be very difficult to set and will get loose in your mounting more often.

There are ways to get a larger look with a single stone and can cost less than a round brilliant. And that is to consider a fancy shape. What is a fancy shape? Any shape other than round. The typical fancy shapes are princess and asscher (square), pear (teardrop), oval (egg), marquise (eye shape), heart, radiant and emerald (rectangular). Fancy shapes are very individual—each person will like something different, and each will look different when you wear them. Oval, pear, and marquise tend to look great on Long thin fingers. For shorter fingers, I would stick with princess or asscher. A radiant or emerald looks pretty nice on both.

If you do want a 1.00 ct that looks larger than a round, then you can choose an oval & pear shape which ideally measure around 7.5 x 5.5, emerald & rad-7x5, marquise 10 x5. However, the princess=5.5, cushion 5.5, asscher 5.5 will actually look smaller at approximately 5.5 mm because they are inherently cut deeper to achieve their maximum optical effects.

As far as value, popularity goes in & out. In the 70’s-90’s marquise and pear was all the rage, then princess and cushion, then radiant and asscher. Now is oval’s turn. So expect to pay a premium for oval brilliant diamond.

When it comes to total weight and value of rounds or fancies, if you have 1, 1.00ct diamond ($8-10k/ct), it will cost and be more valuable than 4, .025ct = 1.00ct ($1500/ct) and that will be much more than 100 .01ct= 1.00cttw ($900/ct) due to rarity of size and the huge differences in price per carat.

When it comes to buying your special someone that important engagement ring, is bigger always better? Well, you know her best or at least you should. Notice the jewelry she already wears, is it thin and dainty or bigger and more of a statement. What is her personality, shy or outgoing? What does she do for a living—does she wear gloves constantly or teach, is she a lawyer or salesperson? How does she dress mostly,, in jeans, in a suit, or casually dressed? What is your lifestyle like—homebody or go out often? Then the all important question is how much can you afford; what do you feel comfortable spending? So you have a little homework and after you watch the rest of my diamond series you will be well on your way to knowing what is right for you & her!

The other thing to keep in mind when buying and choosing between a round & fancy shape besides personal taste is if and when you go to sell your diamond. Which I have a free guide revealing 7 secrets about selling your jewelry, I will put the link in the comments for you to get fully knowledgeable before making such a decision. But as a sneak peak, I will tell you that round will always get more-it is always in style and always in demand. As for fancies, it will depend on what is in style and saleable at that particular time.

My recommendation and my expertise is instead of selling, save money and that value by transforming it into something different. Pears and marquise will not sell these days but they will make gorgeous necklaces and can make a really beautiful freeform ring. Book your Free Rejewelvenate it! Discovery call and transform those old diamonds today!

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