  This paper presents a direct measurement of the decay width of the top quark
using $t\bar{t}$ events in the lepton+jets final state. The data sample was
collected by the ATLAS detector at the LHC in proton-proton collisions at a
centre-of-mass energy of 8 TeV and corresponds to an integrated luminosity of
20.2 fb$^{-1}$. The decay width of the top quark is measured using a template
fit to distributions of kinematic observables associated with the hadronically
and semileptonically decaying top quarks. The result, $\Gamma_t = 1.76 \pm 0.33
(\rm{stat.}) ^{+0.79}_{-0.68} (\rm{syst.})\; \rm{GeV}$ for a top-quark mass of
172.5 GeV, is consistent with the prediction of the Standard Model.
