densit relativa fata de un gaz de referinta se noteaza d(gaz ref.) = M.molec. substanta / M.moleculara gaz de referinta
=> fata de azot (N2), unde M.moleculara N2 = 28 g/mol
=> d(N2) =M(freon) / M(azot)
=> d(N2) = 101 / 28 = 3,60
=> d(aer) = 101 / 28,9 = 3,49