specific weight specific mass specific gravity of liquid
Specific Mass [Density] :
Density is defined as mass per unit volume. Mass is a property.
If ρ = density (kg/m3) ,m = mass (kg), V = volume (m3)
ρ = m / V
Specific Weight :
Specific Weight is defined as weight per unit volume. Weight is a force.
If γ = specific weight (N/m3), ρ = density (kg/m3), g = acceleration of gravity (9.81 m/s2)
γ = ρ g
Specific Gravity [Relative Density] :
Specific Gravity – SG – is a dimensionless unit defined as the ratio of the density of a substance to the density of water – at a specified temperature.
If SG = Specific Gravity of the substance ,ρsubstance = density of the fluid or substance (kg/m3), ρH2O = density of water – normally at temperature 4 oC (kg/m3)
[It is common to use the density of water at 4 oC as a reference since water at this point has its highest density of 1000 kg/m3.]
SG = ρsubstance / ρH2O