A method is presented for in situ resolution calibration of multiple feedback interferometers (MFIs) using two lasers with different feedback levels simultaneously. The laser with weak optical feedback level generates half-wavelength optical fringes, whereas the laser with strong multiple feedback level generates optical nano-fringes. By using this method, the number of displaced optical nano-fringes can be easily counted, and the resolution of the MFIs can be accurately determined. The integrated MFIs can be used to measure displacements and calibrate other displacement sensors.