The fluid density (or mass density) are constantly present in equations of fluid mechanics .

Commonly, the ratio of the mass per unit volume used is Kg/m3

For purists, I met him, I should point out that the density of a substance is the ratio of the density of the material on the density water. This gives us a dimensionless number, without unity, which is the density of this material

Example: The density of water is 1000 Kg/m3

the density of oil is 800 Kg/m3

Density of oil = 800/1000 = 0.8

Water density = 1000/1000 = 1

With Mecaflux

The density of liquids or gases is given in the fluid editor

The editor gives the fluid density of the fluid selected based on its temperature but also its viscosity and saturation vapor pressure