Not to be a pain, but, I have some issues with the stone size chart.
This is the biggest:
Note that the weight for a 10x12 oval is estimated to be 5 carats. This is approximately correct and consistent with other figures I have seen. However, the 10x12 emerald cut and 10x12 radiant cuts are also quoted as 5 carats. This is does not make sense. Observe that if you take the oval face up and the rectangular cuts face up [all three depth tolerances are within the same range], the oval would sit entirely within the rectangles. So there would be extra stone sticking out on the sides for the rectangular cuts. Hence, the rectangular cuts of the same dimensions would be expected to weigh more than the oval. This conclusion is consistent both with my own experience [my 9.9x11.8x6.5 EC weighs 6.39 carats - a 10x12x6.5 EC is in the 1A [top] cut category] and with the calculator, below. The issue is carried through all the weights for these shapes.
The 5 carat weight for a 11x11 trillion is also suspect. I believe it is overstated. Ditto for the heart of the same dimensions [albeit to a lesser degree]. [I am too lazy to do the volume calculations for well cut stones of these shapes at the moment - I'm still sick].
Just my .02 [I hope my explanation was sufficiently transparent to be understandable!]
To get depth ranges for the various shapes [if you don't have them] go to http://www.gemappraisers.com/ and click on "old DIY cut grading" link on the left. Type in the shape and it will give you acceptable ranges for the various measurements for the qulaity cut you are interested in.
Dunno. One guess may be that Wink is using the diamond equivalent weights for the interlap square cut stones [from their site] since they don't specifically list Asschers. I wouldn't worry at those levels - the % and absolute difference is small [and could be accounted for by variations in cut] - unlike the 1.5 carat understatement for the 10x12 EC I noted.
I compared two of my Ashas to the chart and I find the 2 carats are between the 1.5 and 2 range probably somewhere around 1.75. I think the Ashas run a little small compared to diamonds. Do most of you agree, or am I crazy?
I think that the chart is off, rather than the Asha measurements being off. I was curious, so I checked out the measurements of 2 carat princess diamonds on Whiteflash and they are closer to 7mm (like an Asha) than to 7.5mm (on the chart).
The rounds on whiteflash were also slightly smaller than shown on the chart, but there was less difference.
You have to keep in mind that the chart is a pretty broad generalization as the diameter / carat conversion can be vary depending on how shallow or deep the diamond is cut.
My company runs into this problem with the Moissanite stones we sell. We've had customers complain that the 8mm, 2.0ct is bigger than a 2.0ct and smaller than a 2.0ct. In the end it all depends on the stone.
(Although personally I do not feel that a 6x6mm princess is a 1ct but closer to a 1.25ct. I believe I read on BTD's website that one of the gemologists that appraised the princess cut agreed that the 1ct princess was a little big for a 1ct. A 1ct princess is closer to a 5.5x5.5mm. But given the effect of "shrinkage" I'm sure customers don't complain
I think if you stick with the mm size that is comfortable for you and that looks appropriate on your hand, and the corresponding *approximate* carat weight is what you have in mind, then using the mm size when making your choice is the safest way of getting what you want.
This will sound nuts, but I used the amazon chart by printing it and cutting out the ones I thought I liked and taped the cutout to my finger (just rolled up a little bit of tape and stuck it to the back of the cutout, then stuck it onto my ring finger where the stone would sit). This was actually really helpful in figuring out what mm size I wanted!