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When buying pre-loved- How accurate are the online diamond calculators?

Lisa Loves Shiny

Lisa Loves Shiny

Ideal_Rock
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Nov 1, 2007
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Just ballpark if anyone knows. I've looked at the online ones such as this one https://www.omnicalculator.com/other/diamond-weight#diamond-weight-formulas. I've compared them with some GIA reports of OMC diamonds I like and it seems pretty close. Like maybe off by 5%. I think that is probably due to girdle thickness and large culet. Does anyone have any experience with this? Thanks
 
I just tried inputting my two omcs and the 3.6ct was off by about 10% and the 5.68 was off by about 20%. This calculator I found overestimates the ct for the size.
 
I just tried it with my 3.10 carat old mine cut. I put the dimensions in as "cushion" and it estimated 3.73 carats.

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Thanks for the replies. I tried a couple more calculators and some were pretty close and some overestimated. I think antique OMC's vary so much in that they can be in-between round and cushion shaped. Most likely the newer cut "old" OMC's bring a closer result because they are usually cushioned shape. Edited to add that face up size and pleasing facet pattern are more important than weight, but a lot of sellers increase the price based on weight so that's always something to consider.
 
Since mine isn't the cushioniest cushion, I tried mine as an oval and got estimates from 2.56 to 3.46 carats from the same four calculators (truth is 3.10). And of course in many settings you can't even estimate the depth. I'm not a betting woman so I don't personally see myself getting into buying already-set rings if I cared about the stats of the center stone, but I love when people here get unexpected wins!
 
I bout a sapphire and the calculator I used was off by about 5%. Overestimated.
 
OM cuts are highly varied and without expertise is assessing the added weight factor beyond any formula, you will never hit the correct es6timate without you personal experience input. Close is all dealers generally need. A bit of a gamble is inherent and part of the game. This makes consumers a lot less pleased.

Diamonds with with length to width ratios which vary also make it necessary to adjust formulas as length increases from square shapes or from fat pears to long thin pears. The formulas are an art in themselves.
 
oldminer said:
OM cuts are highly varied and without expertise is assessing the added weight factor beyond any formula, you will never hit the correct es6timate without you personal experience input. Close is all dealers generally need. A bit of a gamble is inherent and part of the game. This makes consumers a lot less pleased.

Diamonds with with length to width ratios which vary also make it necessary to adjust formulas as length increases from square shapes or from fat pears to long thin pears. The formulas are an art in themselves.
Click to expand...

Thank you for the expert reply. It is very helpful.
 
I had a ring appraised with three very cushiony OECs/OMCs and the estimates were super close to what GIA said when I got them graded. So a skilled appraiser must have some better math (though they were way off in color and clarity lol)
 
The coefficient for round is .0061 and cushion is .0080 maybe they're using like .007 to estimate?? :lol-2: When I do .007 its close. I think the issue with OM is the depth can be all over.
 
Lisa Loves Shiny said:
Thanks for the replies. I tried a couple more calculators and some were pretty close and some overestimated. I think antique OMC's vary so much in that they can be in-between round and cushion shaped. Most likely the newer cut "old" OMC's bring a closer result because they are usually cushioned shape. Edited to add that face up size and pleasing facet pattern are more important than weight, but a lot of sellers increase the price based on weight so that's always something to consider.
Click to expand...

Please share link to more accurate online calculators you found so we can try at home. Thanks, great thread.
 
Round diamonds have an 0.0061 formula factor which includes diamond's specific gravity times a geometric round faceted gemstone shape shape factor. Diamond has an SG of 3.52m and that geometric factor for all round gems shaped similar to how one cuts a diamond is .001733. 0.0061 is a convenient shortcut, but more useful to know the formula applies to a much broader formula.

Old mine cuts can be just a step more complex than an OEC or they can become a nearly different shape, blocky, near square, elongated with and without corners, high crowned, bulging pavilions. I have see stones that measured up to a factor of .0077. They were really like cobblestones in an ancient city, not what we would usually want in a modern item.. Yet, perfectly acceptable in an old piece where they were original.
 
@LightBright - After you calculate the diamond weight with the source I listed- please make sure you look at the carat range in parenthesis. Hope that helps.
 
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