ISO 15112:2011 provides the means for energy determination of natural gas by measurement or by calculation, and describes the related techniques and measures that are necessary to take. The calculation of thermal energy is based on the separate measurement of the quantity, either by mass or by volume, of gas transferred and its measured or calculated calorific value. The general means of calculating uncertainties are also given.Only systems currently in use are described.ISO 15112:2011 applies to any gas-measuring station from domestic to very large high-pressure transmission.New techniques are not excluded, provided their proven performance is equivalent to, or better than, that of those techniques referred to in ISO 15112:2011.Gas-measuring systems are not the subject of ISO 15112:2011.