A device for determination of the H2 content of H2/natural gas mixtures comprises an input interface configured to read in a calorific value of a first H2/natural gas mixture from a delivery station of a gas grid, an input interface configured to introduce a second H2/natural gas mixture into the device; a proton-conducting layer fluidically connected to the input interface of the second H2/natural gas mixture and configured to permit determination of a current-voltage characteristic, a volumetric flow rate sensor configured to determine a volumetric flow rate of the second H2/natural gas mixture into the proton-conducting layer, and a control apparatus connected to the proton-conducting layer, the input interface of the second H2/natural gas mixture, and the volumetric flow sensor. The control apparatus is configured to determine whether there is a hydrogen depletion of the proton-conducting layer, and output the current calorific value of the second H2/natural gas mixture.