An aqueous solution of 99mTc was standardized by means of 4πce(LS)-γ and 4πce(PC)-γ coincidence counting. The activity concentration was obtained by efficiency extrapolation relying on four different variation techniques. In both setups, fast digitizers were used for data acquisition. Detected events were recorded in list mode format, and their coincidence relationship was analyzed in the subsequent offline analysis. The combined result was used to participate in an international comparison using the Transfer Instrument of the International Reference System. •99mTc was standardized by 4πce(LS)-γ and 4πce(PC)-γ coincidence counting.•Digitizer-based DAQ in combination with offline coincidence analysis was used.•Activity concentration was derived by various efficiency variation methods.•The results from different methods are in good agreement with each other.