Physics
Specific gravity
Divide the density by the density of water. The units cancel, leaving a dimensionless number that is 1 for water itself.
The Formula
SG = rho / rho_water
Divide the density by the density of water. The units cancel, leaving a dimensionless number that is 1 for water itself.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| SG | Specific gravity | dimensionless | Dimensionless. Water is 1 by definition, so 2 means twice as dense. |
| rho water | Density of water | g/cm3 or kg/m3 | 1.0 g/cm3 or 1000 kg/m3 at about 4 C, its maximum. |
What Each Symbol Means
SGdimensionless
Specific gravity
Dimensionless. Water is 1 by definition, so 2 means twice as dense.
rho waterg/cm3 or kg/m3
Density of water
1.0 g/cm3 or 1000 kg/m3 at about 4 C, its maximum.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate density page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Density, filed under Science. Every number the guide produces comes from substituting into this one line.