How to measure the size and the approximate weight of a mounted diamond:
When a diamond is fixed in a ring or setting you can estimate
the diameter between the prongs on opposite sides of a stone
With a professional measuring tool, gauge estimator or a brass calipers
you will find the size / dimensions of set / mounted diamonds,
the inside and outside diameter, depth + thickness.
brass callipers Leveridge
You can buy it at about +- US $ 7
at www.stantonbooks.com
or you have it already in your toolbox
The diamond size is the key to estimate the carat weight of diamonds.
To estimate the diameter in a closed setting and the carat weight of
fancy shaped diamonds we advice to go to a professional jeweler.