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