6.5 Carat Radiant (10.78×10.78×6.9mm)

Diamond details

Actual size of a 6.5 carat Radiant
Actual size
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Shape: Radiant
Weight: 6.5 carat
Price: check here »
L×W×D: 10.78 × 10.78 × 6.9 mm
Depth: 64% OK
L/W ratio: 1
Face-up size:
This diamond LOOKS its weight!
This 6.5 carat Radiant has a face-up area of approx. 110.4 mm², which falls within the normal range for 6.5ct Radiants. A face-up area is the area of the girdle plane and tells you how big the stone looks when viewed from the top (as set in a ring). Face-up size of this diamond is as you would expect of a 6.5ct Radiant → learn more

Actual Diamond Size

Here you can see how big 6.5 carat Radiant (10.78×10.78×6.9mm) actually is and how it would appear on a ring and finger. Adjust the ring and finger size to get an idea of how it would look on your finger. To choose another diamond or to change diamond parameters click here.
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Ring: Skin tone:
Ring image
6.5ct Radiant diamond of actual size
Ring width: 3.0 mm
Side view of Radiant diamond Side view of a ring
Ring diameter: 16.9 mm
Finger image
Ring image
6.5ct Radiant diamond of actual size
64 mm
Your settings
Skin tone
Ring diameter
16.9 mm
Ring width
3.0 mm
Finger length
64 mm
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To see how this 6.5 carat Radiant (10.78×10.78×6.9mm) compares to other diamonds, click here.

Buying Guide: Radiant cut

For Radiants, there are no universally accepted standards in terms of cut quality. You should stay within the recommended parameter ranges defined below. In general, avoid too deep or too shallow stones and make sure the corners are even and symmetrical.

How much does a 6.5ct Radiant cost?

It depends. The value of a diamond is determined by a combination of its unique characteristics - the famous 4Cs (Cut, Color, Clarity, and Carat). It can get complicated, but you can quickly check the price range for Radiant diamonds of around 6.5 carats by clicking here »

The search results will show you Radiant cut diamonds from 6.3 to 6.7 carats with all the recommended parameters already preselected in order to give you the best value.

Note: The supply of Radiant diamonds at around 6.5 carats might not be that abundant, so you might want to expand the search parameters.

Best Value For Money Recommendation

For 6.5 carat Radiant:
  • Color:
    • H if platinum/white gold solitaire setting
    • J if yellow gold solitaire setting
  • SI2 clarity
  • At least Good polish/symmetry
  • GIA or AGS report
  • If possible, "buy shy" [explain]
For best deals on 6.5ct Radiant check the recommended online stores (all provide actual diamond images):
Look for:
  • Color: H or higher [depends on a setting]
  • Clarity: SI or better [explain]
  • Cut parameters:
    • Depth: 59% - 70%
    • Table: 58% - 70%
    • Polish/Symmetry: Good or better
    • Length-to-width ratio: 1.00 - 1.35
  • Diamonds certified by GIA or AGS [explain]
  • Eye-clean
Watch out for:
  • Non-symmetrical corners
  • Inclusions visible to the naked eye
  • Extremely thin or extremely thick girdle
  • Fair or Poor symmetry
  • Strong blue fluorescence [explain]
  • Diamonds without GIA or AGS certification [explain]
Where to buy?
Online-only stores will always offer better prices compared to bricks & mortar stores, their main drawback, however, is that you rarely get the opportunity to visually inspect the diamond before purchasing. Luckily, this is not always the case. A few reputable online retailers (see above) are now providing actual Hi-Res photos of the diamonds they're selling, making it easy and safe to shop online. For best value, buy online.

Note: Seeing a high quality photo of the actual diamond before purchasing online is a must. This goes especially for fancy shapes as the market is quite flooded with ugly looking stones.

Additional Diamond Info

Radiant cut is a combination of Emerald elegance and Round brilliance. It's a brilliant alternative to the Emerald, developed and patented in 1970s by Henry Grossbard. Radiants are quite similar to Princesses, but usually more rectangular in shape and with angled corners.

General size appearance:

Radiant cuts typically look smaller when viewed from the top compared to other shapes of the same carat weight.
Shape: Radiant cut
Also known as: Square or Rectangular Cut Cornered Modified Brilliant
Cutting style: Mixed
Facets: usually between 62 - 70
Signature shape characteristics: Rectangular or square shape with cropped corners
Carat weight: 6.5 ct
Gram weight: 1.3 g (0.0459 ounces)
Points: 650 pts
Measurements (L/W/D): 10.78 x 10.78 x 6.9 mm
Length: 10.78 mm
Width: 10.78 mm
Depth: 6.9 mm
Depth percentage: 64%
Recommended depth percentage: 59 - 70%
Length-to-width ratio: 1
Typical length-to-width ratio: between 1.00 and 1.35
Face-up area: 110.4 mm² (±4%)
Face-up area per carat: 16.98 mm²/ct
Face-up size: Normal for 6.5 carat Radiant
Volume: 369.32 mm³
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Depth percentage for 6.5 carat Radiant (10.78×10.78×6.9mm)

Depth percentage of Radiant cut is the ratio of the total depth (measured from table to culet) to its width. The total depth percentage of this diamond is 64%, which is OK.

Depth percentage for radiants is calculated with the following formula:
Depth % = (total depth ÷ width) × 100

6.5 carat Radiant (10.78×10.78×6.9mm) depth %:
Total depth: 6.9 mm
Width = 10.78 mm
Depth % = (6.9 ÷ 10.78 ) × 100 = 64%

About Depth Percentage
Depth percentage is one of the most important measurements as it plays a critical role in diamond's brilliance and appearance. If a diamond is cut too deep or too shallow, light leaks out, making the stone less brilliant and fiery. Deep cuts also add hidden weight.

Recommended depth percentage range for Radiant cuts is between 59% and 70%. Diamonds that fall out of this range are generally less desirable and usually best to be avoided.

Face-up size evaluation for 6.5 carat Radiant (10.78×10.78×6.9mm)

The face-up size of this 6.5 carat Radiant (10.78×10.78×6.9mm) is within the normal range for 6.5ct diamonds of this shape. Compared to 6.5ct Radiant reference diamond (see below), this diamond is of adequate size when viewed from the top. In short, all is OK, this diamond looks its weight.

The importance of face-up size
Diamonds are sold by weight (carats), but it's important to understand that weight doesn't equally translate into physical size, especially spread. Two diamonds of the same carat weight can vary greatly in spread, meaning that one diamond can appear larger than the other, even though they weight exactly the same.

Proper face-up size should play an important role when buying a diamond. When a diamond is set in a ring, your eyes will only see the face-up area, so you should make sure it's of adequate size. Adequate size also indicates a good cut, meaning better light performance. For example, if given a choice between a poorly cut 6.5 carat Radiant with less sparkle and the same face-up size as a well cut 6.2ct Radiant, which one would you choose?

The bottom line: A diamond must look its weight. This one does. Thumbs up.

6.5 carat Radiant reference diamond
Since there are no specific ideal proportions defined for Radiant cuts, an estimation formula is used to calculate the Radiant reference diamond.
Weight: 6.5ct
Depth: 64%
L/W ratio: 1
Calculated values:
Length: 10.78 mm
Width: 10.78 mm
Depth: 6.9 mm
*Est. face-up area: 110.4 mm²
Note: Radiant diamonds with face-up area of within 9% lower and 12% higher than reference Radiant diamond area are considered to be of adequate face-up size.
* Estimated Face-up area: Face-up area of Radiant cuts is only an estimation (±4%). Due to uniqueness of each stone, it's impossible to accurately calculate face-up area given only a diamond's measurements.
To learn more about diamond size evaluation, click here.

Face-up Area For Radiants

Face-up area is a measure of the size of the diamond when viewed from above. It tells you how big the diamond is at the girdle plane. It's important for a diamond to have sufficient face-up size for its carat weight.

Note: Due to geometrical uniqueness of fancy shaped diamonds, it's impossible to accurately calculate face-up area given only length and width. Surface area for radiant cuts is therefore only an estimation, usually within 4% accurate.

For more info see carat weight vs face-up size

Face-up Area per Carat

Face-up area per carat is calculated by dividing face-up area of the diamond with its carat weight. It tells you how many square millimeters of the top surface area a diamond is showing or would show for 1 carat weight. This can be useful when comparing stones of similar weights as it tells you how much spread per carat you will get.

Note: Face-up size does not linearly grow with carat weight, which means the heavier the stone, the smaller its face-up area per carat (e.g., 1ct stone will have higher face-up area per carat than 2ct stone).

Face-up area per carat for 6.5ct Radiant (10.78×10.78×6.9mm):
Top surface area = 110.4 mm²
Weight = 6.5ct

Face-up area per carat = 110.4 ÷ 6.5 = 16.98mm²/ct

Color Recommendation For 6.5ct Radiant

Radiants show color quite strongly, so it's recommended not to go too low on the color scale. The choice of color also depends on a setting:

Solitaire Small side-stones Substantial side-stones
White gold/Platinum H+ G+ same as side-stones+
Yellow gold J+ I+ same as side-stones+
e.g. pave setting e.g. three-stone setting
Note: If side-stones are of any significant size (like in three-stone settings), you should at least match the color of the center stone with the color of the side stones, otherwise the center stone might look out of place (a bit "off-white").

For best value, go with the minimum recommended color for a particular type of setting. Color variations between H graded and higher colored Radiant cuts are so slight that it's almost impossible to tell the difference, especially when diamonds are mounted. The difference in price, however, can be quite considerable.

Clarity Recommendation For 6.5ct Radiant

Radiants are quite forgiving of inclusions, so you can go relatively low on a clarity scale, as long as the diamond is eye-clean. SI1, SI2 clarity or higher is recommended.

Note: You can always go lower in clarity, but it's going to get increasingly difficult to find an eye-clean Radiant below the minimum recommended SI2 grade.

For best value, go with the lowest clarity possible that is still eye-clean. If a diamond is eye-clean, it doesn't matter, if it's flawless or SI2. It will look the same, provided all other characteristics are the same.
About Diamond Clarity
Diamond clarity refers to the presence and visual appearance of the flaws inside a diamond (called inclusions) or on its surface (called blemishes). Clarity tells you to what degree these imperfections are present.

The amount of inclusions and blemishes is directly correlated to a diamond's value. Fewer imperfections mean higher price and vice versa.

Gemological laboratories grade diamond clarity as Flawless (FL), Internally Flawless (IF), Very Very Slightly Included (VVS1,VVS2), Very Slightly Included (VS1,VS2), Slightly Included (SI1,SI2), and Included (I1,I2,I3).

GIA and AGS Certified Diamonds

Professional and unbiased assessment of diamond characteristics is stated on a diamond grading report, commonly referred to as a certificate. Certificate, while not 100% reliable, is essential in determining a diamond's value.

The standard for diamond grading is pretty much set by GIA - Gemological Institute of America. They are the most reputable and consistent lab in the industry. AGS (American Gemological Society) is not far behind.

If a diamond is not certified by GIA or AGS, you can be pretty much certain that you are looking at lesser quality than indicated. This puts you in a bad position of not knowing the true diamond characteristics, which almost always results in overpaying. That is why a certificate from a well-respected grading lab is so important.

The bottom line: Make sure to always buy a diamond certified by either GIA or AGS. That's the only way of truly getting the quality you expect.

Diamonds with Blue Fluorescence

Blue fluorescence can have a positive, negative, or zero effect on a diamond. Diamonds in the lower color range (H or lower) can benefit from it, as it can make them look whiter, more colorless. On the other hand, strong fluorescence can cause a stone (especially in the higher color range D-G) to appear hazy or milky under certain light conditions. One of the biggest benefits of fluorescent diamonds is that they generally cost less.

GIA grades fluorescence as None, Faint, Medium, Strong, and Very Strong.

Faint fluorescence will have zero effect on color and overall appearance. Fluorescence of this type is not an issue and shouldn't be a purchasing factor.

Medium fluorescence will in most cases have zero to very small influence on color and overall appearance, however, colorless diamonds can sometimes exhibit negative effects and should be examined in different light conditions before purchasing.

Strong/Very Strong fluorescence requires caution. Generally, it's not a good idea to buy a colorless diamond with Strong/Very Strong fluorescence. As for lower color diamonds, even they can sometimes look hazy with strong fluorescence, so never buy a stone with this type of fluorescence without careful visual inspection.

If you're interested in fluorescent diamonds that have been carefully examined and do not display any negative effects of fluorescence, I recommend Brian Gavin's Blue Diamonds. Those are definitely top of the line and a great value.

Diamonds Without GIA or AGS Certificates

The problem with diamond grading labs other than GIA or AGS is that they are looser and more inconsistent in their grading standards. A GIA color H is an IGI color G and an EGL/HRD color F. The same goes for clarity.

While it's true that IGI, EGL, and HRD diamonds are sold at a discount, you can be certain that the same stones would cost less, if they would be certified by GIA or AGS. Why? Because they would get lower grades and thus lower price. Lower than discounted IGI, EGL, and HRD stones with higher grades.

Diamond merchants use IGI, EGL, HRD, and alike to maximize their profits. They know they can sell diamonds with inflated grades for more, even if they're sold at a substantial discounts. Some merchants also use their in-house certification, usually for the sole purpose of increasing their profits. These kinds of certificates are meaningless.
The bottom line: If you don't want to overpay and want to know exactly what kind of quality you're getting, then avoid diamonds without GIA or AGS certification.

Buying shy

Buying shy means choosing a diamond that falls just under the full-carat or half-carat mark. So instead of 1ct stone you go for 0.95ct; instead of 1.5ct you go for 1.4ct, and so on.

Because diamond prices jump dramatically at full-carat and half-carat weights, you can save a considerable amount of money when buying shy. Going up to 10% down in weight will result in a slight difference in size, but so slight it'll barely be noticed, if at all. To check this for yourself, use this site to compare different sizes.

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