An output driver calibration circuit determines calibration values for configuring adjustable impedance output drivers. Output drivers are calibrated by generating a first variable count in response to comparing a reference voltage to a first voltage at a calibration terminal when an external load is connected. A first pull-up impedance circuit is varied in response to a first variable count and varying an impedance in a second variable pull-up impedance circuit in response to the first variable count. A second variable count is generated responsive to comparing the reference voltage to a second voltage at a reference node between the second variable pull-up impedance circuit and a serially connected to a variable pull-down impedance circuit. The impedance to the variable pull-down impedance circuit is varied in response to the second variable count. The first and second variable counts for configuring the output drivers are output when a steady state is achieved.