Bolometric fluxes for 118 dwarfs and subdwarfs with 4000K less than Teff less than 7000K and +0.5 less than (Fe/H) less than -3.5 are derived by integrating UBVRIJHK photometry. For these stars (typical of the galactic and globular cluster main sequences) at least 80% of the energy emitted is measured by those bands. A grid of theoretical model line-blanketed flux distributions ws used in order to estimate the flux out-side these photometric bands. The method, based on the use of synthetic magnitudes, provides bolometric fluxes with an estimated uncertainty in the order of 2%. The result obtained have been used to calibrate the bolometric flux versus K, (V-K) and Fe/H), in order to derive an expression of general application. A by-product of this study is the bolometric correction for main sequence stars, which is tabulated for different metallicities. Comparisons of these results with those obtained by other authors are presented and discussed.