  We use high spatial resolution maps of stellar mass and infrared flux of the
Large Magellanic Cloud (LMC) to calibrate a conversion between 3.6 and 4.5
micron fluxes and stellar mass, M_* = 10^{5.65} * F_{3.6}^{2.85} *
F_{4.5}^{-1.85} * (D/0.05)^2 M_solar, where fluxes are in Jy and D is the
luminosity distance to the source in Mpc, and to provide an approximate
empirical estimate of the fractional internal uncertainty in M_* of
0.3*sqrt{N/10^6}, where N is the number of stars in the region. We find
evidence that young stars and hot dust contaminate the measurements, but
attempts to remove this contamination using data that is far superior than what
is generally available for unresolved galaxies resulted in marginal gains in
accuracy. The scatter among mass estimates for regions in the LMC is comparable
to that found by previous investigators when modeling composite populations,
and so we conclude that our simple conversion is as precise as possible for the
data and models currently available. Our results allow for a reasonably
bottom-heavy initial mass function, such as Salpeter or heavier, and moderately
disfavor lighter versions such as a diet-Salpeter or Chabrier initial mass
function.

Astrophysics of Galaxies