Density
The density at all points of a homogeneous object equals its total mass divided by its total volume. The mass is normally measured with a scale or balance; the volume may be measured directly (from the geometry of the object) or by the displacement of a fluid. To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively. Similarly, hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object.
Saltwater intrusion
The figure shows the Ghyben–Herzberg relation. In the equation, formula_1 the thickness of the freshwater zone above sea level is represented as formula_2 and that below sea level is represented as formula_3. The two thicknesses formula_2 and formula_3, are related by formula_6 and formula_7 where formula_6 is the density of freshwater and formula_9 is the density of saltwater. Freshwater has a density of about 1.000 grams per cubic centimeter (g/cm) at 20 °C, whereas that of seawater is about 1.025 g/cm. The equation can be simplified to formula_10.