  We conducted interferometric observations with the CHARA Array of transiting
super-Earth host HD 97658 and measured its limb-darkened angular diameter to be
$\theta_{\text{LD}}=0.314\pm0.004$ mas. The combination of the angular diameter
with the Gaia EDR3 parallax value with zero-point correction
($\pi=46.412\pm0.022$ mas, $d=21.546\pm0.011$ pc) yields a physical radius of
$R_\star=0.728\pm0.008$ $R_\odot$. We also measured the bolometric flux of the
star to be $F_\text{bol}=2.42\pm 0.05\times 10^{-8}$erg s$^{-1}$ cm$^{-2}$,
which, together with angular size, allows a measurement of the effective
temperature $T_{\text{eff}}=5212\pm43$ K. Our directly determined physical
stellar properties are in good agreement with previous estimates derived from
spectroscopy. We used our measurements in combination with stellar evolutionary
models and properties of the transit of HD 97658 b to determine the mass and
age of HD 97658 as well as constrain the properties of the planet. Our results
and our analysis of the TESS lightcurve on the planet (TOI-1821) corroborate
previous studies of this system with tighter uncertainties.
