  Stellar spectra obtained with Radial Velocity Spectrometer on-board Gaia will
enable determination of projected rotational velocities (v sin i) from
rotational broadening of spectral lines. To estimate the accuracy with which v
sin i can be determined for different stellar types and as a function of
magnitude, we perform simulations in which "observed" spectra (as obtained from
Gaia RVS simulator) are fitted with Kurucz spectra from template library using
the least square method. We compare results on the v sin i accuracy as obtained
in the case of spectra differing only in v sin i and in the case of a more
general spectral mismatch (in T_eff, log g, [Fe/H]).
