The standardized gemstone size chart is a chart that provides the average size of a gem according to the weight and shape of the stone. The sizes provided on the chart are an average and vary depending on the specific type of gem and the cut of the stone.
Colored gems are commonly cut with more volume than clear gems, so they are likely to weigh more than the weight listed on the chart. The density of the stone can also make the actual weight of the stone vary from the weight listed on the chart. As a result, different types of gems cut in the same proportions are likely to have a variation in weight.