In order to provide a measuring device for determining stoichiometric ratios when burning hydrocarbons by means of which stoichiometric ratios can be determined easily and reliably when burning hydrocarbons, it is proposed that a sensor be provided to detect an intensity of a first fluorescent radiation from C--H molecular fragments arising during the burning and a sensor be provided to detect an intensity of a second fluorescent radiation from molecular fragments arising during the burning and comprising only C atoms, that the sensors generate an intensity-dependent first and second sensor signal, respectively, on the basis of the first and the second fluorescent radiation, and that an evaluation circuit be provided which generates an output signal corresponding to a stoichiometric ratio from a ratio between the intensities of the first and the second fluorescent radiation.