  Estimates for the sedimentation rate of realistic ice crystals at sizes
smaller than 100 $\mu$m are presented. These calculations, which exploit new
results for the capacitance of ice crystals, are compared with laboratory
studies and found to be in good agreement. The results highlight a weakness in
contemporary ice particle fall speed parameterisations for very small crystals,
which can lead to sedimentation rates being overestimated by a factor of two.
The theoretical approach applied here may also be useful for calculating the
sedimentation rate and mobility of non-spherical aerosol particles.
