Direct angular size measurements of the G0IV subgiant \eta Boo from the Palomar Testbed Interferometer are presented , with limb-darkened angular size of \theta _ { LD } = 2.1894 ^ { +0.0055 } _ { -0.0140 } mas , which indicate a linear radius of R = 2.672 \pm 0.028 R _ { \odot } .
A bolometric flux estimate of F _ { BOL } = 22.1 \pm 0.28 \times 10 ^ { -7 } erg cm ^ { -2 } s ^ { -1 } is computed , which indicates an effective temperature of T _ { EFF } = 6100 \pm 28 K and luminosity of L = 8.89 \pm 0.16 L _ { \odot } for this object .
Similar data are established for a check star , HD 121860 .
The \eta Boo results are compared to , and confirm , similar parameters established by the MOST asteroseismology satellite .
In conjunction with the mass estimate from the MOST investigation , a surface gravity of \log g = 3.817 \pm 0.016 [ cm s ^ { -2 } ] is established for \eta Boo .