Weigh your stone in air, then submerged in water, and this tool works out its specific gravity — and which gemstone species that SG could belong to.
Both weights should come from the same scale, in the same unit (grams or carats — just be consistent).
SG results are matched against typical published ranges for common species — treatments, inclusions, and mixed compositions can shift a real stone's SG slightly outside textbook values, so use this alongside other tests, not in place of them.
Specific gravity (SG) is the ratio of a gemstone’s weight to the weight of an equal volume of water. It’s a dimensionless number — diamond sits at about 3.52, sapphire at roughly 4.00, and amber down near 1.08 — and it stays remarkably consistent for each mineral species regardless of the stone’s size or cut.
That consistency is exactly why gemologists rely on it: two stones can look identical but carry very different specific gravities. Combined with refractive index and hardness, SG narrows an unknown stone down to a short list of candidates in minutes, using nothing more than a scale, a cup of water, and a piece of thread.
Specific gravity is the ratio of a gemstone's weight in air to the weight of an equal volume of water. It's a fixed, measurable property of each mineral species — for example, diamond is about 3.52, ruby and sapphire about 3.95–4.03, and emerald about 2.67–2.80 — which makes it one of the most useful identification values in gemology.
Weigh the stone in air, then weigh it suspended in water, and divide: SG = weight in air ÷ (weight in air − weight in water). The water measurement is lower because the water buoys the stone up by exactly the weight of the water it displaces. This free calculator does the math for you and matches the result against typical species ranges.
Yes. Any scale accurate to 0.01 g (most kitchen or jewelry scales work), a cup of water, and a thin thread are enough. Tare the cup and thread first, weigh the stone in air, then suspend it fully submerged without touching the cup's sides or bottom. Enter both numbers above.
No — SG narrows the field to a few candidates, but treatments, inclusions, and mixed compositions can shift a real stone slightly outside textbook ranges. Always confirm with at least one other test, such as refractive index, before making a final identification or purchase decision.