  The interference between Cabibbo-favoured and Cabibbo-suppressed $B\to D\pi$
decay amplitudes provides sensitivity to the CKM angle $\gamma$. The relative
size of the interfering amplitudes is an important ingredient in the
determination of $\gamma$. Using branching fractions from various $B\to Dh$
decays, and the measured value for $r_{B}^{DK}$, the magnitude of the amplitude
ratio of $B^+\to D^0\pi^+$ and $B^+\to \bar{D}^0\pi^+$ decays is estimated to
be $r_{B}^{D\pi} = 0.0053 \pm 0.0007$.
