If you know how to measure and have the proper tools, relatively accurate (+/- 10%) carat weights can be estimated from gem measurements and observations.
Round standard brilliant cut diamonds
Measuring unset gemstones is much easier than attempting to measure gems in settings. Measuring bezel set gemstones is virtually impossible. Estimating gems in settings that do not expose the pavilion is even more unreliable.
Calipers, micrometers and leveridge gauges are ideal for measuring gemstones accurately. Knowing how to read the various scales and dials requires some practice.
Factors that influence gemstone carat weight estimates
- Gem material – specific gravity
- Gem cut/shape factor & deviation
- Girdle thickness
- Crown height
- Table size relative to gem size
- pavilion bulge
- Culet size
Note: Even with accurate measurements, estimates should not be relied upon for purchasing gems or diamonds. Insist on a certified weighing of an unset gemstone on a high quality calibrated gem scale