A theoretical model of an elongated field reversed configuration (FRC) adiabatically compressed to high density by an imploding liner is presented. Compression is assumed to be self-similar, equal along length and radius, and is accomplished by means of a shaped liner. In particular, the model here takes into account the special magnetic topology of the FRC and the non-uniformity of the radial plasma profiles in order to quantify final to initial compression ratios of the fluid quantities.