The problem is that the charts that I have found don''t have a cushion cut mm to carat chart. The closest that I have found is a Princess cut conversion chart. I know the difference between the 2 cuts, but would the Princess cut chart work (more or less) for a cushion cut?
Sometimes cushions face up smaller. sometimes that''s a good thing and sometimes it''s not. Don''t worry too much if it looks like a 1.75... if it speaks to you and you are happy with the face up size...it''s fine.
Cushions aren''t as straightforward as RBs because there isn''t an ideal cut for them. My own cushion is 2.01 carats, and it faces up at 7.81 x 6.93. I saw several cushions that faced up larger and weighed less, and many that faced up smaller and weighed more.
You just have to trust your eye and see what speaks to you with cushions.
Since I deal mostly with gemstones I often try to use this to get an idea of what mm I''m dealing with, and a rough idea of what it would translate to with a diamond. It''s a little bit off, but it gives you an idea once it''s at 100%. I think it''s closer to real life at 90%. Anyway, I find it helpful. Linky