+.It Fl B Ar records
+The number of 1 kB blocks per volume. Not normally required, as
+.Nm
+can detect end-of-media. When the specified size is reached,
+.Nm
+waits for you to change the volume. This option overrides
+the calculation of tape size based on length and density.
+If compression is on this limits the size of the compressed
+output per volume.