An impedance calibration circuit may be provided. The impedance calibration circuit may include an adjusting circuit. The adjusting circuit may be configured to generate a calibration code based on a variation voltage, which may be applied to a calibration node coupled to a calibration pad, and a reference voltage. The adjusting circuit may be configured to apply a voltage, which may be generated according to a control signal generated based on an operational voltage mode in accordance with the calibration code, to the calibration node. The adjusting circuit may include a plurality of leg circuits. At least one of the leg circuits may include a plurality of legs configured to be selectively coupled to the calibration node based on the control signal.