We have calibrated the effective temperatures of the low main sequence stars ranging spectral types from F0 to K5 versus [Fe/H] and colours (B-V), (R-I), (V-R), (V-I), (V-K), (J-H), (J-K) and ubvy-β, using a large sample of dwarfs and subdwarfs. The effective temperatures, scaled to direct T_eff_ determinations via reliable angular diameter measurements, were derived applying the InfraRed Flux Method with the new grid of atmosphere models developed by Kurucz (1993). We have fitted polynomial functions of the form θ_eff_=P(colour,[Fe/H]) using the least squares method. The precision of the fits ranges from 30K for (V-K) to 154K for (J-H). The new relations have been compared to previous calibrations. We also provide the empirical intrinsic colours (U-B), (B-V), (R-I), (V-R), (V-I), (V-K), (J-H), (J-K) and β, in the ranges: 4000K[Fe/H]>-2.5.