  A most desirable feature of a standard candle to estimate astronomical
distances is robustness against changes in metallicity and age. It is argued
that the radii of main sequence stars with spectral types from solar to A0 show
predictable changes with metallicity, and detectable changes with evolution.
Such stars populate the solar neighborhood, and therefore benefit from
measurements of angular diameters. Also, reliable determinations of their
masses and radii are available from observations of eclipsing binaries. Three
empirical relationships are defined and suggested for estimating distances to
dwarfs from only BVK photometry. Comparison with HIPPARCOS trigonometric
parallaxes shows that the method provides errors of about 15% for a particular
star, which can be reduced to roughly 1.5% when applied to young clusters (age
<~ 1-2 Gyr) with ~ 100 stars of the appropriate spectral types. If reddening is
unknown, main sequence stars with effective temperatures close to 8000 K can
constrain it, although an estimate of R=A(V)/E(B-V) is required.
