Certain aspects of the present disclosure generally relate to magnetometer calibration. In some aspects, a device may obtain multiple sets of magnetic field measurements corresponding to multiple local magnetic field strengths, wherein each set of magnetic field measurements is measured in association with an unknown local magnetic field strength. The device may calculate multiple error values using the multiple sets of magnetic field measurements, estimated values of the multiple local magnetic field strengths, and estimated hard iron bias values. The device may identify a set of hard iron bias values for magnetometer calibration based at least in part on comparing the multiple error values. The device may calibrate a magnetometer using the identified set of hard iron bias values.