We construct high signal-to-noise "template" spectra by co-adding hundreds of spectra of nearby dwarfs spanning K7 to M4, taken with Keck/HIRES as part of the California Planet Search. We identify several spectral regions in the visible (370-800 nm) that are sensitive to the stellar luminosity and metallicity. We use these regions to develop a spectral calibration method to measure the mass, metallicity, and distance of low-mass stars, without the requirement of geometric parallaxes. Testing our method on a sample of nearby M dwarfs, we show that we can reproduce stellar masses to about 8%-10%, metallicity to similar to 0.15 dex, and distance to 11%. We were able to make use of HIRES spectra obtained as part of the radial velocity monitoring of the star KOI-314 to derive a new mass estimate of 0.57 +/- 0.05 M-circle dot, a radius of 0.54 +/- 0.05 R-circle dot, a metallicity, [Fe/H], of -0.28 +/- 0.10, and a distance of 66.5 +/- 7.3 pc. Using HARPS archival data and combining our spectral method with constraints from transit observations, we are also able to derive the stellar properties of GJ 3470, a transiting planet hosting M dwarf. We estimate a mass of 0.53 +/- 0.05 M-circle dot, a radius of 0.50 +/- 0.05 R-circle dot, a metallicity, [Fe/H], of 0.12 +/- 0.12, and a distance of 29.9+/-(3.7)(3.4) pc.
