You seem to know a lot about Emerald cuts...answer me this if you will...

what size is a 4 carat EC comparbale to in Round Brilliants?

That was a weirdly worded sentence! YIKES! What I want to know is how big will a 4 carat EC appear. Will it look similar to a 2 carat round or a 4 carat round. I know that EC's look smaller than they are because they are cut so deep, but im not sure how "big" four carats really is...

so i turn to you....

I always thought that emerald cuts look larger because of their length...at least a well cut one anyway. A one carat emerald cut is around 7 x 5mm, but a one carat round is about 6.5mm.

For more accuracy than a conversion chart on interlap's site, I used a diamond seach engine to pull up various sizes of 4 carat stones and here is a sampling of the sizes that I found:

Emerald cuts:
3.98 carats: 10.55-8.50x4.64
4.03 carats: 10.20-7.73-5.66
4.0 carats: 10.15-7.74-5.69
4.04 carats: 11.65-7.45-4.83
4.03 carats: 10.94-7.75-5.13

Rounds:
4.0 carats: 10.13-10.07x6.25
4.01 carats: 9.94-9.98-6.33
4.01 carats: 10.36*10.44*6.09
4.0 carats: 10.21-10.27-6.25