  Using simple dimensional arguments for both spiral and elliptical galaxies,
we present formulas to derive an estimate of the halo spin parameter $\lambda$
for any real galaxy, in terms of common observational parameters. This allows a
rough estimate of $\lambda$, which we apply to a large volume limited sample of
galaxies taken from the SDSS data base. The large numbers involved (11,597)
allow the derivation of reliable $\lambda$ distributions, as signal adds up
significantly in spite of the errors in the inferences for particular galaxies.
We find that if the observed distribution of $\lambda$ is modeled with a
log-normal function, as often done for this distribution in dark matter halos
that appear in cosmological simulations, we obtain parameters $\lambda_{0}=0.04
\pm 0.005$ and $\sigma_{\lambda}=0.51 \pm 0.05$, interestingly consistent with
values derived from simulations. For spirals, we find a good correlation
between empirical values of $\lambda$ and visually assigned Hubble types,
highlighting the potential of this physical parameter as an objective
classification tool.
