Emerald rings are valued using the 4 "Cs", same as diamond rings and other precious gemstones.
Below are the most important factors in valuing emerald rings:
The weight of the emerald(s) set upon and within the ring is measured in carats. The most common carat weights are between .5 carats and 1.5 carats.
The but of an emerald ring doesn't refer to the shape of the emerald, it refers to the quality of the cut and it's ability to interact with or refact light.
The clarity of an emerald ring is measured in the same manner as other precious gemstones. Internally flawless emerald rings are the highest clarity.
Emerald rings may only be the color green. Deep green emerald rings typically fetch the highest prices.