Topic summary
Number density
The number density (symbol: n or ρN) is an intensive quantity used to describe the degree of concentration of countable objects (particles, molecules, phonons, cells, galaxies, etc.) in physical space: three-dimensionalvolumetric number density, two-dimensionalareal number density, or one-dimensionallinear number density. Population density is an example of areal number density. The term number concentration (symbol: lowercasen, or C, to avoid confusion with amount of substance indicated by uppercaseN) is sometimes used in chemistry for the same quantity, particularly when comparing with other concentrations.