A novel kind of pycnometer was designed for liquid density measurements suitable to be used over wide ranges of temperature and pressure. Two similar pycnometers have been manufactured and tested with n-nonane 99.7mol% in the temperature range from 233K to 313K at pressure lower than 10MPa. To validate the procedure, the experimental values of density of an n-nonane sample have been compared with the density values given in the literature by means of the En number. The density uncertainty of n-nonane is found to be 0.16kgm−3 (0.02%) in the temperature range from 253K to 313K and lower than 0.07% between 233K and 243K over the whole pressure range tested.