A gas meter (10) determining the calorific value of the gas passing through the meter is disclosed. The meter includes a reaction chamber (28) that draws gas from the gas flow path and an air intake (30). The calorific value is determined using a resistor (36), coated with a catalyst material, that forms part of a wheatstone bridge circuit. Oxidation of the gas/air mixture on the surface of the resistor (36) causes a temperature and resistance change dependent on the calorific value of the gas that can be detected by the wheatstone bridge.