  The distance of the Virgo cluster is derived in the B band from the 21
cm-line width-absolute magnitude relation. The latter is calibrated using 18
spirals with Cepheid distances mainly from HST. The calibration is applied to a
complete sample of non-peculiar spirals with i>45 deg and lying within the
optical (n=49) or X-ray (n=35) contour of the cluster, resulting in a mean
cluster distance of (m-M)_0=31.58+/-0.24 mag (external error) or 20.7+/-2.4
Mpc. The mean distance of subcluster A is 0.46+/-0.18 mag smaller than that of
subcluster B, but the individual distances of the members of the two
substructures show considerable overlap. The distance modulus is corrected by
-0.07 mag for the fact that cluster members have lower H I-surface fluxes and
are redder in (B-I) at a given line width than the (field) calibrators.
Different sources of the B magnitudes and line widths have little effect on the
resulting distance. Different precepts for the internal-absorption correction
change the result by no more than +/-0.17 mag. The individual distances of the
cluster members do not show any dependence on recession velocity, inclination,
Hubble type or line width. The dependence on apparent magnitude reflects the
considerable depth effect of the cluster. The adopted distance is in good
agreement with independent distance determinations of the cluster. Combining
the cluster distance with the corrected cluster velocity of 1142+/-61 km/s
gives H_0=55+/-7 km/s/Mpc (external error). If the Virgo cluster distance is
inserted into the tight Hubble diagram of clusters out to 11000 km/s using
relative distances to the Virgo cluster one obtains a global value of
H_0=57+/-7 km/s/Mpc.
