The conformational distribution of glycerol is still an open question both in gas and in liquid phase. Density functional calculations on different conformers of glycerol are reported and compared to the experimental infrared spectra of the gas and of the liquid. The experimental infrared spectra of gas and liquid glycerol are fitted by a linear combination of the single conformer ab initio spectra, obtaining the relative conformer concentrations. For the gas the results are in agreement with electron diffraction experiments and with molecular dynamics simulation data. The conformational distribution of glycerol in liquid phase is less accurate but always indicative. Some results about the role of the intramolecular hydrogen bonding in stabilization and in structural features of the conformers an discussed.