Specific Gravity Calculator for Minerals and Gemstones (Hydrostatic Weighing)
Specific gravity, density and volume of a mineral, rock or gemstone from its weight in air and its weight hanging in water, plus its weight in carats.
Results
The dashed line marks the value you entered.
What this tool does
Weigh the specimen in air, then again hanging in water: the loss of weight equals the weight of the water it displaces, and specific gravity is the weight in air divided by that loss. It is one of the most useful clues for identifying a mineral without damaging it — quartz is about 2.65, calcite 2.71, corundum (ruby, sapphire) about 4.0, gold near 19.3. Hang the stone on a thin thread, make sure no air bubbles cling to it, and use a balance that reads to 0.01 g or better for small stones.
Formula
SG = W_air ÷ (W_air − W_water) · volume = (W_air − W_water) ÷ ρ_water
Variables
| Symbol | Meaning | Unit |
|---|---|---|
wa | Weight in air | g |
ww | Weight suspended in water | g |
rw | Density of the water (0.998 at 20 °C) | g/cm³ |
SG | Specific gravity | — |
DE | Density of the sample | g/cm³ |
VO | Volume of the sample | cm³ |
CT | Weight in carats (1 ct = 0.2 g) | ct |
Worked example
- Weight in air25 g
- Weight suspended in water15.6 g
- Density of the water (0.998 at 20 °C)0.998 g/cm³
- Specific gravity2.660
- Density of the sample2.654 g/cm³
- Volume of the sample9.419 cm³
- Weight in carats (1 ct = 0.2 g)125.00 ct
Limitations
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.