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Large spectroscopic surveys of the Milky Way need to be calibrated against asample of benchmark stars to ensure the reliable determination of atmosphericparameters. We present new fundamental stellar parameters of seven giant andsubgiant stars that will serve as benchmarks. The aim is to reach a precisionof 1% in the effective temperature. This precision is essential for accuratedeterminations of the full set of fundamental parameters and abundances ofstars observed by the surveys. We observed HD121370 (etaBoo), HD161797 (muHer),HD175955, HD182736, HD185351, HD188512 (betaAql), and HD189349 using the highangular resolution optical interferometric instrument PAVO/CHARA. Thelimb-darkening corrections were determined from 3D model atmospheres based onthe STAGGER grid. The Teff were determined directly from the Stefan-Boltzmannrelation, with an iterative procedure to interpolate over tables of bolometriccorrections. We estimated surface gravities from comparisons to Dartmouthstellar evolution model tracks. The spectroscopic observations were collectedfrom the ELODIE and FIES spectrographs. We estimated metallicities ([Fe/H])from a 1D non-local thermodynamic equilibrium (NLTE) abundance analysis ofunblended lines of neutral and singly ionised iron. For six of the seven starswe measure Teff to better than 1%. For one star, HD189349, the uncertainty inTeff is 2% due to an uncertain bolometric flux. We do not recommend this staras a benchmark until this measurement can be improved. Median uncertainties forall stars in logg and [Fe/H]} are 0.034dex and 0.07dex, respectively. All thefundamental stellar parameters were based on consistently combininginterferometric observations, 3D limb-darkening modelling and spectroscopicanalysis. This paper follows our previous papers including dwarfs andmetal-poor stars.

Fundamental stellar parameters of benchmark stars from CHARA interferometry -- III. Giant and subgiant stars