6ct Cushion (10.59×10.59×6.78) vs 3ct Round (9×9×5.65)

Diamond size comparison

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Actual size of 6ct Cushion diamond
Actual size
sample image
Actual size of 3ct Round diamond
Actual size
sample image
6 ct Cushion (10.59×10.59×6.78mm) 3 ct Round (9×9×5.65mm)
Cutting style
(modified) brilliant
6 ct
3 ct
10.59×10.59×6.78 mm
9×9×5.65 mm
Total depth
64% OK
62.8% too deep!
L/W ratio
Face-up size
This diamond LOOKS its weight!
This diamond does NOT look its weight!
Actual diamond size
Actual diamond size
Before purchasing a diamond, one should make sure it looks its weight. It's important to understand that carat weight does not equal face-up size.

Two diamonds of exactly the same weight (and shape) can vary quite considerably in face-up size. This depends on the proportions of the cut (e.g., deep cuts will face up smaller).

Here you can see the actual sizes of 6ct Cushion (10.59×10.59×6.78mm) and 3ct Round (9×9×5.65mm) as they would appear on a ring and finger.

Adjust the ring and finger size to get an idea of how these stones would look on your finger. To choose different diamonds or to change diamond parameters click here.
Ring: Skin tone:
Ring width: 3.0 mm
Left finger image
Ring on a left finger
6ct Cushion on a left ring
64 mm
Right finger image
Ring on a right finger
3ct Round on a right ring
Your settings
Skin tone
Ring diameter
16.9 mm
Ring width
3.0 mm
Finger length
64 mm
Ring diameter: 16.9 mm
6ct Cushion side view Side view of ring
3ct Round side view Side view of ring
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Face-up area
100.93 mm²  (±5%)
63.62 mm² 
Face-up area is a measure of the size of the diamond when viewed from the top (as set in a ring).

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.
Face-up size outline
Face-up size outline
6ct Cushion (10.59×10.59×6.78mm)
3ct Round (9×9×5.65mm)
Difference: 37.31mm² (59%)
6 carat Cushion (10.59×10.59×6.78mm) has approx. 59% more face-up area than 3 carat Round (9×9×5.65mm).
Face-up area per carat
16.82 mm²/ct
21.21 mm²/ct
To learn about the accuracy of these numbers, click here.

Quick Buying Guide

Diamond prices vary greatly as they depend on the combination of unique characteristics (4Cs - Cut, Color, Clarity, and Carat). For best value, it's important to choose the combination that will reduce the price without having a negative impact on appearance.

Each shape has its own recommended balance of qualities that will give you the most bang for your buck. Below is a quick buying guide to give you an idea, but for more detailed explanation, please see the complete buying guides for the respective diamonds (links below).
6ct Cushion (10.59×10.59×6.78mm)
3ct Round (9×9×5.65mm)
Price (best value)
Min. clarity
SI1 or better
SI or better
Min. color (platinum setting)
Min. color (yellow gold setting)
Depth percentage
59 - 70%
58 - 62.5%
Table percentage
56 - 70%
53 - 58%
Length-to-width ratio
1.00 - 1.35
1.00 - 1.02
Min. polish/symmetry
Good or better
Good or better
 Detailed buying guide

Additional Info

6ct Cushion (10.59×10.59×6.78mm)
3ct Round (9×9×5.65mm)
Face-up size
Normal for 6 carat Cushion
Too small for 3 carat Round
usually 58
58 (57 if no culet)
10.59 mm
9 mm
10.59 mm
9 mm
6.78 mm
5.65 mm
Gram weight
1.2 g (0.0423 ounces)
0.6 g (0.0212 ounces)
600 pts
300 pts
340.91 mm³
170.45 mm³

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Depth percentage for 6 carat Cushion (10.59×10.59×6.78mm)

Depth percentage of Cushion 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. (Recommended depth percentage for Cushions is between 59% and 70%)

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

6 carat Cushion (10.59×10.59×6.78mm) depth %:
Total depth: 6.78 mm
Width = 10.59 mm
Depth % = (6.78 ÷ 10.59 ) × 100 = 64%

Depth percentage for 3 carat Round (9×9×5.65mm)

Depth percentage of Round cut is the ratio of the total depth (measured from table to culet) to its average diameter. The total depth percentage of this diamond is 62.8%, which is too deep!. (Recommended depth percentage for Rounds is between 58% and 62.5%)

Depth percentage for rounds is calculated with the following formula:
Depth % = (total depth ÷ average diameter) × 100

3 carat Round (9×9×5.65mm) depth %:
Total depth: 5.65 mm
Average diameter = (9 + 9) ÷ 2 = 9 mm
Depth % = (5.65 ÷ 9 ) × 100 = 62.8%

About Depth Percentage
Depth percentage is one of the most important measurements as it plays a critical role in diamond's 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.

Diamonds that fall out of recommended depth range are generally less desirable and usually best to be avoided.

Face-up size evaluation for 6 carat Cushion (10.59×10.59×6.78mm)

The face-up size of this 6 carat Cushion (10.59×10.59×6.78mm) is within the normal range for 6ct diamonds of this shape. Compared to 6ct Cushion 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 carat Cushion with less sparkle and the same face-up size as a well cut 5.7ct Cushion, which one would you choose?

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

6 carat Cushion reference diamond
Since there are no specific ideal proportions defined for Cushion cuts, an estimation formula is used to calculate the Cushion reference diamond.
Weight: 6ct
Depth: 64%
L/W ratio: 1
Calculated values:
Length: 10.59 mm
Width: 10.59 mm
Depth: 6.78 mm
*Est. face-up area: 100.93 mm²
Note: Cushion diamonds with face-up area of within 9% lower and 12% higher than reference Cushion diamond area are considered to be of adequate face-up size.
* Estimated Face-up area: Face-up area of Cushion cuts is only an estimation (±5%). 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 size evaluation for 3 carat Round (9×9×5.65mm)

The face-up size of this 3 carat Round (9×9×5.65mm) is out of normal range for 3ct diamonds of this shape. A well cut 3ct Round should have an average diameter between 9.13 and 9.51 mm. Compared to 3 carat Round reference diamond, this diamond appears too small when viewed from the top, which makes it a chubby.

A chubby is a diamond with hidden extra weight that looks smaller than it should when viewed from the top. Hidden weight is typically a result of a poor cut usually linked to oversized girdle, deeper pavilion, and/or steeper crown.

In order to maximize profits, diamond cutters tend to retain as much weight from the rough as possible. This practice, however, can have detrimental effects on the stone's face-up size and its optical qualities. Poorly proportioned stones look duller and sparkle less than well cut stones. Chubby stones also look smaller.

The bottom line: One should never sacrifice beauty for weight. You probably don't want to pay for extra weight that doesn't add anything to the beauty. You want a stone that looks its weight. This one doesn't - sizewise, it looks like a well cut 2.65ct diamond.

3 carat Round reference diamond
3ct Round reference diamond is calculated from the following ideal proportions:
Table: 57%
Crown angle: 34°
Pavilion angle: 40.7°
Girdle: 2.8%
Star length: 50%
Lower half-length: 80%
Culet: None
Calculated values:
Depth: 60.3%
Crown height: 14.5%
Pavilion height: 43%
For 3 carat weight:
Diameter: 9.37 mm
Face-up area: 68.96 mm²
Note: Round diamonds with face-up area of within 5% lower and 3% higher than reference Round diamond area are considered to be of adequate face-up size.
To learn more about diamond size evaluation, click here.

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 6ct Cushion (10.59×10.59×6.78mm):
Top surface area = 100.93 mm²
Weight = 6ct

Face-up area per carat = 100.93 ÷ 6 = 16.82mm²/ct

Face-up area per carat for 3ct Round (9×9×5.65mm):
Top surface area = 63.62 mm²
Weight = 3ct

Face-up area per carat = 63.62 ÷ 3 = 21.21mm²/ct

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