We propose a method of measuring the electron temperature T-e in mesoscopic conductors and demonstrate experimentally its applicability to micron-size graphene devices in the linear-response regime (T-e approximate to T, the bath temperature). The method can be especially useful in case of overheating, T-e > T. It is based on analysis of the correlation function of mesoscopic conductance fluctuations. Although the fluctuation amplitude strongly depends on the details of electron scattering in graphene, we show that T-e extracted from the correlation function is insensitive to these details.