  We present a measurement of the total decay width of the top quark using
events with top-antitop-quark pair candidates reconstructed in the final state
with one charged lepton and four or more hadronic jets. We use the full
Tevatron Run II data set of $\sqrt{s} = 1.96$ TeV proton-antiproton collisions
recorded by the CDF II detector. The top-quark mass and the mass of the
hadronically-decaying $W$ boson are reconstructed for each event and compared
with distributions derived from simulated signal and background samples to
extract the top-quark width (\gmt) and the energy scale of the calorimeter jets
with {\it in-situ} calibration. For a top-quark mass $\mtop = \gevcc{172.5}$,
we find $1.10<\gmt<\gev{4.05}$ at 68% confidence level, which is in agreement
with the standard-model expectation of \gev{1.3} and is the most precise direct
measurement of the top-quark width to date.
