  We calculate directly determined values for effective temperature ($T_{\rm
EFF}$) and radius ($R$) for 191 giant stars based upon high resolution angular
size measurements from optical interferometry at the Palomar Testbed
Interferometer. Narrow- to wide-band photometry data for the giants are used to
establish bolometric fluxes and luminosities through spectral energy
distribution fitting, which allow for homogeneously establishing an assessment
of spectral type and dereddened $V_{\rm 0}-K_{\rm 0}$ color; these two
parameters are used as calibration indices for establishing trends in $T_{\rm
EFF}$ and $R$. Spectral types range from G0III to M7.75III, $V_{\rm 0}-K_{\rm
0}$ from 1.9 to 8.5. For the $V_{\rm 0}-K_{\rm 0} = \{1.9,6.5\}$ range, median
$T_{\rm EFF}$ uncertainties in the fit of effective temperature versus color
are found to be less than 50K; over this range, $T_{\rm EFF}$ drops from 5050K
to 3225K. Linear sizes are found to be largely constant at 11 $R_\odot$ from
G0III to K0III, increasing linearly with subtype to 50 $R_\odot$ at K5III, and
then further increasing linearly to 150 $R_\odot$ by M8III. Three examples of
the utility of this data set are presented: first, a fully empirical
Hertzsprung-Russell Diagram is constructed and examined against stellar
evolution models; second, values for stellar mass are inferred based on
measures of $R$ and literature values for $\log g$. Finally, an improved
calibration of an angular size prediction tool, based upon $V$ and $K$ values
for a star, is presented.
