  Accurate and precise values of radii and masses of stars are needed to
correctly estimate properties of extrasolar planets. We examine the effect of
uncertainties in stellar model parameters on estimates of the masses, radii and
average densities of solar-type stars. We find that in the absence of seismic
data on solar-like oscillations, stellar masses can be determined to a greater
accuracy than either stellar radii or densities; but to get reasonably accurate
results the effective temperature, log g and metallicity must be measured to
high precision. When seismic data are available, stellar density is the most
well determined property, followed by radius, with mass the least well
determined property. Uncertainties in stellar convection, quantified in terms
of uncertainties in the value of the mixing length parameter, cause the most
significant errors in the estimates of stellar properties.
