  The 16.1MeV 2+ resonance in 12C situated slightly above the proton threshold
can decay by proton-, $\alpha$-, and $\gamma$ emission. The partial width for
proton emission cannot be directly measured due to the low proton energy and
the small branching ratio. Instead it must be indirectly derived from other
observables. However, due to several inconsistent data the derived partial
width varies by almost a factor 2 dependent on the data used. Here we trace the
majority of this inconsistency to different measurements of the $(p,\alpha)$
cross sections. We have remeasured this cross section using modern large area
silicon strip detectors allowing to measure all final state particles, which
circumvents a normalization issue affecting some of the previous measurements.
Based on this we determine $\Gamma_{p}$ = 21.0(13)eV. We discuss the
implications for other observables related to the 16.1 MeV $2^{+}$ resonance
and for isospin symmetry in the $A=12$ system. In addition, we conclude that
the dataset currently used for the NACRE and NACRE II evaluation of the
$^{11}\mathrm{B}(p,3\alpha)$ reaction should be scaled by a factor of 2/3. This
impacts the reaction rate accordingly.
