Gemstone Density Calculator

Submerging the stone lets water buoyancy do the volume measurement for you -- Archimedes' principle says the weight lost underwater equals the weight of the water displaced, and that displaced volume is exactly the stone's own volume. Dividing the stone's dry weight by that volume-equivalent weight loss gives specific gravity, a property that doesn't change no matter how the stone is cut or polished.

They're the same number here for practical purposes -- water's density at 4degC is defined as exactly 1 gram per cubic centimeter, so a stone's specific gravity (its weight relative to an equal volume of water) and its density in g/cm3 come out numerically identical. Gemologists usually talk in specific gravity because it's unitless and comparable across any measurement system.

Not on its own -- several gem species share overlapping specific gravity ranges (topaz and spinel both sit close to 3.5-3.6, for instance), so the Possible Gem Matches list is meant as a narrowing tool rather than a definitive ID. The comparison ranges themselves come from the Gemological Institute of America's published per-species property data (for example, GIA lists diamond at SG 3.52 and emerald at SG 2.72). Pairing the SG reading with refractive index, hardness, or a loupe inspection for inclusions gives a much more confident identification.

Volume and Specific Gravity are both driven by the gap between the two readings, not by either one in isolation -- that gap is the weight of water the stone displaced, which is what Archimedes' principle actually measures. Weight in Air and Weight in Water each move Volume by an equal and opposite amount, so it's the weight "lost" underwater, not the raw size of either reading, that tells you the stone's volume.