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Calculating Depth W/out Any Measuring Devices?


boogafish
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Hello. I recently purchased a 2.25 ct oval diamond from an estate sale which has these measurements: 10.3 length and 6.5 width. That's all I know. I'm trying to find out if there is a calculatable correlation between carat weight and the depth using these dimensions because I have no real good way to measure the depth until I get it appraised.

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We're missing the third measurement- the actual depth.

To calculate depth percentage, dive the smallest number ( the depth) by the middle number.

For example:

An oval measuring

12mm length x 10mm width x 6mm depth is 60% depth ratio

That is what his question is: What is the depth (Not the depth ratio). Is there a formula that uses the three parameters he currently has: Length, Width, and Carat Weight, that would allow him to roughly caclulate/estimate the depth of the diamond?

 

Based upon way too many math classes my gut feeling is Yes its possible, but without knowing the actual formulas I won't be much help. Basically the carat weight is equal to a known volume? 100 different 1Ct diamonds should all displace the same amount of volume regadless of their shape, right? (Unless the density of a diamond varies based upon other factors)

 

Interesting question though.

 

Brian

Edited by BrianB
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In a word, no.

 

The classic weight formula for ovals is the average diameter squared x depth x 0.0067 = weight

 

This will get you an answer within, say, 15% either way and you can use simple algebra to move around the unknown. That margin of error will be due to variations in the girdle and the bulge of the crown and pavilion. The real problem is the source of the data. Length and width are usually relatively straightforward to measure directly but what’s the source of that 2.25ct. measurement? If the stone was loose it could be accurately weighed but then the depth could be directly measured as well. Obviously, direct measurement would be the best way to get the depth and this whole discussion becomes moot. I’m going to guess that the weight came from the advertisement and that it was calculated, not weighed so lets add another, say 20% either way for that. Maybe more because we don’t know if the person doing the calculations had any clue what they were doing. Back to the math class, we’re up to a 70% margin of error (35% each direction). That’s huge, and it renders the above formula basically useless for the question at hand.

 

Neil

Edited by denverappraiser
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  • 2 years later...

Yes, you can determine the depth from what you know. Appraising jewelry is detective work and requires an understanding of deducing unknown factors based on what information you have, so if we accept the 2.25c weight of the oval diamond as accurate, and the 10.3mm length and 6.5mm width as accurate, then we can use the same formula to determine depth--within a close tolerance. 10.3 + 6.5 = 16.8 divided by 2 equals an average diameter of 8.4mm. Calculate the weight finding formula: 8.4 X 8.4 X depth X .0065 + 6% to adjust for the normally thick girdles of oval cuts of this size = 2.25c. So, to solve for the unknown: depth = (2.25-6%) '/. .0065 '/. 8.4 '/. 8.4 or depth = 4.611mm. If we don't adjust for extra girdle thickness, then the depth ranges to 4.90mm, but 30 years as an appraiser says the 4.611 is the better bet. Hope this helps.

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Yes, you can determine the depth from what you know. Appraising jewelry is detective work and requires an understanding of deducing unknown factors based on what information you have, so if we accept the 2.25c weight of the oval diamond as accurate, and the 10.3mm length and 6.5mm width as accurate, then we can use the same formula to determine depth--within a close tolerance. 10.3 + 6.5 = 16.8 divided by 2 equals an average diameter of 8.4mm. Calculate the weight finding formula: 8.4 X 8.4 X depth X .0065 + 6% to adjust for the normally thick girdles of oval cuts of this size = 2.25c. So, to solve for the unknown: depth = (2.25-6%) '/. .0065 '/. 8.4 '/. 8.4 or depth = 4.611mm. If we don't adjust for extra girdle thickness, then the depth ranges to 4.90mm, but 30 years as an appraiser says the 4.611 is the better bet. Hope this helps.

 

Funny, first you have to be a gemologist, chemist and mineralogist to understand a lot of this stuff and now we you are adding mathematician. I'll never catch up to all this stuff. LOL Nice equation though.

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