AbstractThe relation of the surface brightness, a parameter related to the apparent magnitude and the angular diameter of a star, with a colour index is used to determine various stellar parameters. Eclipsing spectroscopic binaries can even be used as a distance indicator. In this work, we use a number of low-mass eclipsing binaries, whose parameters have been accurately determined, to refine the Barnes-Evans–like relation F_V − (I_c − K) introduced by Amado et al. (1999), a relation more suitable for the low temperature of these cool stars.