  We propose a phenomenological equation for the vortex line density in
rotating Bose-Einstein condensates as a function of the angular speed. This
equation provides a simple description of the gross features of the increase in
vortex number from the appearance of the first vortex to the theoretical
rigid-body result for high vortex density, and allows one to compare with
analogous situations in superfluid helium, after the suitable changes in the
relevant parameters are made.
