Specific Gravity Calculator
Last updated: September 2026
Weigh the stone dry, weigh it suspended in water, and read off the specific gravity — then see which species that value does not rule out.
grams, on a dry pan
grams, fully submerged, no bubbles
— enter both weights
SG = weight in air ÷ (weight in air − weight in water). The denominator is the weight of the water the stone displaced. No temperature or buoyancy correction is applied, which is worth about ±0.01 at room temperature — fine for separating species, not fine for splitting two that overlap.
What this does and does not cover
The table behind this calculator is 132 gem species and varieties, spanning SG 1.05 to 8.20. It is not a rock or mineral database. Most field finds are aggregates — jasper, chert, basalt, slag, concretions — and they are not in here. If your value matches nothing, that is a real result and usually means the material is outside this table rather than that you measured it wrong.
Specific gravity alone rarely settles an identification, because ranges overlap. It narrows. To go further you need a second property — hardness, streak, or a refractive index if the stone has a polished face.
- How to measure specific gravity — the method, the arithmetic, and the errors that move the third decimal
- Specific gravity chart — every species in one sortable table
- Mohs hardness chart — the usual second reading
- The open dataset — this table as CSV and JSON, CC BY 4.0