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40ct Ruby (Round, 20.45×20.45mm, Red) vs 31ct Diamond (Round, 20.42×20.42mm, White)


Quick summary: When looked from above (face-up position), 40ct Ruby (20.45×20.45mm, round cut) appears 0.3% larger than 31ct Diamond (20.42×20.42mm, round cut). See below how they compare side-by-side on a ring and finger.

40ct Ruby (round cut)
vs
 31ct Diamond (round cut)
red
 
white
20.45×20.45 mm 20.42×20.42 mm
actual size
Actual size of 40ct Ruby (round cut, 20.45×20.45mm, Red color)   Actual size of 31ct Diamond (round cut, 20.42×20.42mm, White color)
 
Actual size is set for screen
Ring: Skin tone:
Ring width: 3.0 mm
Left finger image
Ring on left finger
Red 40ct Ruby (round cut, 20.45×20.45mm) on a left ring and finger
64 mm
Right finger image
Ring on a right finger
White 31ct Diamond (round cut, 20.42×20.42mm) on a right ring and finger
Your settings
Ring
 Gold
Skin tone
 Light
Ring diameter
 16.9 mm
Ring width
 3.0 mm
Finger length
 64 mm
Finger coverage
 122% vs 121%
Saved...
Ring diameter: 16.9 mm
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Actual sizes of 40ct Ruby Round (20.45×20.45mm, Red) and 31ct Diamond Round (20.42×20.42mm, White) as they would appear on a ring and finger. Adjust the ring and finger size to get an idea of how these gemstones would look on your finger.

Where to buy?

For certified gemstones, high-end gemstone jewelry, and birthstone jewelry, see Blue Nile

Face-up Size

All things being equal, Ruby will face-up smaller than Diamond for a given carat weight, because it has higher specific gravity (4 vs. 3.52 - this means it's "heavier" compared to Diamond of the same size). Face-up size also depends heavily on the proportions of the cut.

Face-up area is a measure of the size of the gem when viewed from above (as set in a ring). It tells you how big the gem is at the girdle plane.


40 Ct Ruby (Round) 31 Ct Diamond (Round)
20.45×20.45 mm vs 20.42×20.42 mm
328.46 mm²   327.49 mm²
Face-up size outline for 40ct Ruby (20.45×20.45mm, round cut)
Face-up size outline for 31ct Diamond (20.42×20.42mm, round cut)
40ct Ruby Round (20.45×20.45mm)
31ct Diamond Round (20.42×20.42mm)
Difference: 0.3% (0.97 mm²)
40ct Ruby (Round, 20.45×20.45mm) has approx. 0.3% more face-up area than 31ct Diamond (Round, 20.42×20.42mm).


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