  Determining the physical properties of microlensing events depends on having
accurate angular sizes of the source star. Using long-baseline optical
interferometry we are able to measure the angular sizes of nearby stars with
uncertainties $\leq 2\%$. We present empirically derived relations of angular
diameters that are calibrated using both a sample of dwarfs/subgiants and a
sample of giant stars. These relations are functions of five color indices in
the visible and near-infrared, and have uncertainties of 1.8-6.5% depending on
the color used. We find that a combined sample of both main-sequence and
evolved stars of A-K spectral types is well fit by a single relation for each
color considered. We find that in the colors considered, metallicity does not
play a statistically significant role in predicting stellar size, leading to a
means of predicting observed sizes of stars from color alone.
