According to one disclosed embodiment, an on-chip resistor calibration circuit includes an RC oscillator having a test resistor and a precision capacitor as elements, a counter, and a reference clock. In one embodiment, an RC oscillator generates a waveform having a period dependent upon the resistance of the test resistor and the capacitance of the precision capacitor. In such an embodiment, a counter and a reference clock may be configured to measure the period of the waveform. Using a pre-determined capacitance of the precision capacitor, a resistance of the test resistor may be determined. In another embodiment, an RC oscillator generates first and second waveforms through use of an additional capacitor that can be switched in and out of the RC oscillator circuit. Using a pre-determined capacitance of the precision capacitor, an RC product of the test resistor and the additional capacitor may be determined.