Specific gravity is a dimensionless unit defined as the ratio of the density of a substance to the density of water - at a specified temperature and can be expressed as. SG = ρsubstance / ρH2O . We calculate as follows:
0.789 = ρsubstance / 1000 kg/m^3
ρsubstance = 789 kg / m^3
Hope this answers the question. Have a nice day.