An output driver impedance calibration circuit which is used to make I/O (input/output) off chip driver characteristics, for a plurality of output driver circuits, alike on the same chip. The output impedance of an input/output driver circuit is calibrated by providing an external target impedance reference (it could be a multiple of the actual target output impedance), multiple devices in the output stage of the I/O driver circuit, a circuit to determine the value of the actual output impedance as compared with its target output impedance and a determination of when to stop the calibration process.