  We present a detailed evaluation of the total semileptonic B meson width in
terms of |V_{cb}| and heavy quark parameters (quark masses and the expectation
values of local heavy quark operators). Special attention is given to
perturbative corrections which can precisely be calculated in a scheme with a
hard Wilsonian cutoff at a scale around 1GeV appropriate for the OPE, and to
the potential impact of higher-order power corrections. We point out that the
latter require control over possible contributions from four-quark operators
containing charm quark fields. Analytical expressions are given which allow
evaluating the width with various choices of parameters; ready-to-use
expressions showing the dependence on the heavy quark parameters are presented
as well. We illustrate these results by commenting on how these parameters can
be extracted and what accuracy is likely to be achievable in the near future.
