A gas meter for determining a gas mixture consumption is revealed which determines sensor signal values proportional to a flow rate, this gas meter being calibrated as an energy measuring unit. The calibration is based on a basic gas mixture. During the measurement of the gas consumption, a measured energy consumption value is multiplied by a correction factor which takes account, at least approximately, of the calorific value of a supplied gas mixture, this calorific value being determined by an external unit. By this means, it is possible, using a simple and cost-efficient gas meter, to determine the effective supplied energy and to bill costs according to the supply.