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We calculate directly determined values for effective temperature ($T_{\rmEFF}$) and radius ($R$) for 191 giant stars based upon high resolution angularsize measurements from optical interferometry at the Palomar TestbedInterferometer. Narrow- to wide-band photometry data for the giants are used toestablish bolometric fluxes and luminosities through spectral energydistribution fitting, which allow for homogeneously establishing an assessmentof spectral type and dereddened $V_{\rm 0}-K_{\rm 0}$ color; these twoparameters are used as calibration indices for establishing trends in $T_{\rmEFF}$ and $R$. Spectral types range from G0III to M7.75III, $V_{\rm 0}-K_{\rm0}$ 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 colorare found to be less than 50K; over this range, $T_{\rm EFF}$ drops from 5050Kto 3225K. Linear sizes are found to be largely constant at 11 $R_\odot$ fromG0III to K0III, increasing linearly with subtype to 50 $R_\odot$ at K5III, andthen further increasing linearly to 150 $R_\odot$ by M8III. Three examples ofthe utility of this data set are presented: first, a fully empiricalHertzsprung-Russell Diagram is constructed and examined against stellarevolution models; second, values for stellar mass are inferred based onmeasures of $R$ and literature values for $\log g$. Finally, an improvedcalibration of an angular size prediction tool, based upon $V$ and $K$ valuesfor a star, is presented.

Direct Measurements of Giant Star Effective Temperatures and Linear Radii: Calibration Against Spectral Types and V-K Color