Three‐component magnetic data are derivable from measurements of one single component of the magnetic field over a plane. The technique involves computation of the double‐Fourier‐series coefficients of the measured magnetic anomaly, multiplication of the coefficients by a filter operator, and, finally, evaluation of the magnetic components by taking the inverse Fourier transform. The desired filter operator is obtained from a simple relationship between the components of a potential field. The scheme has been tested with excellent results on the fields of a vertical prismatic model.