Carat per carat high quality emeralds are close to diamonds
One carat equals one fifth of one gram
Always think in terms of cost-per-carat.
Emeralds under 1/2 carat are sold by millimeter, not by the carat.
A carat is a carat. One carat equals one-fifth of one gram. This does not mean, however, that carats cost the same. Larger stones tend to carry a higher per-carat cost due to the scarcity of top quality emeralds in bigger sizes. Therefore, it is a good idea to think in terms of price per carat, rather than total cost. A couple other tips concerning weight:
Beware of "Total weight" price tags. A pendant may have multiple stones on it bringing the total weight to well over one carat, but you want to know the price per carat of the individual stones on the pendant. Always ask the jeweler for such pricing.
Emeralds under 1/2 carat are sold by size, not weight. Stones in this weight category are listed in millimeter size.
Remember that as emeralds increase in weight, their size becomes unpredictable, so it’s a good idea to compare stones of the same weight against one another.
Emeralds are far less dense than gems like diamonds or rubies. A one carat emerald will be quite a bit larger than a one carat ruby or diamond.
A good rule of thumb is to multiply the price-per carat of a particular stone by the carat weight to determine exactly what the total cost of the stone should be.