An energy meter for measuring parameters of fuel gas. The meter has a gas inlet and outlet and a central tube along which the gas flows from inlet to outlet. Ultra-sound transducers and a control form a system whereby the speed of ultra-sound signals traveling through the gas between the transducers is measured and used in the control to calculate the volume of gas which is passed through the meter. The ultra-sound signals pass through apertures in the walls of chambers containing the transducers. Another ultra-sound transducer in the chamber which is connected to the control acts as an emitter and receiver of ultra-sound signals reflected by reflectors. These signals travel through the fuel gas in the chamber and their attenuation is observed and measured by the control when they are received by the transducer. The measured attenuation is used to derive the calorific value and/or Wobbe index of the gas. The control uses the volume of gas and the calorific value and/or Wobbe index to derive the amount of energy in the gas.