A time-to-digital converter system has at least one time-to-digital converter comprising an oscillator, a counter being driven by the oscillator, an evaluation block connected to the counter and configured for determining a time difference associated with a start signal and a stop signal, and a histogram block with a number of bins for recording entries associated with the time difference. The system can be calibrated by operating or preparing to operate the time-to-digital converter system with a measurement clock signal defining a measurement interval, providing a calibration clock signal having a frequency higher than the measurement clock signal by a predefined ratio, using a selected clock edge of the calibration clock signal as the start signal and a subsequent clock edge of the calibration clock signal as the stop signal. The evaluation block determines a calibration time difference based on the respective clock edges of the calibration clock signal used as the start signal and the stop signal. A time measure associated with a counter step of the counter is determined based on the predefined ratio and the calibration time difference.