An updated version of the EUV-TEC proxy, describing the total primary ionisation of the upper atmosphere, is calculated from satellite-borne EUV measurements. Regional number densities of the background model atmosphere consisting of four major constituents are taken from the NRLMSISE-00 climatology. Furthermore, a first estimate of a global thermospheric heating rate is calculated from the absorbed energy. For the calculations the Lambert-Beer law is used to describe the decrease of the radiation along their way through the atmosphere. The EUV-TEC proxy is compared against the global mean total electron content (TEC), obtained from vertical TEC maps derived from GPS data. Strong correlations between these indices are found on different time scales. Results show that the EUV-TEC proxy describes the ionospheric variability better than the conventional solar index F10.7, especially at short time scales of days to weeks.