  This paper suggests using the configurational temperature $\Tc$ for
quantifying how far an active-matter system is from thermal equilibrium. We
measure this ``distance'' by the ratio of the systemic temperature $\Ts$ to
$\Tc$, where $\Ts$ is the canonical-ensemble temperature for which the average
potential energy is equal to that of the active-matter system. $\Tc$ is
``local'' in the sense that it is the average of a function, which only depends
on how the potential energy varies in the vicinity of a given configuration; in
contrast $\Ts$ is a global quantity. The quantity $\Ts/\Tc$ is straightforward
to evaluate in a computer simulation; equilibrium simulations in conjunction
with a single steady-state active-matter configuration are enough to determine
$\Ts/\Tc$. We validate the suggestion that $\Ts/\Tc$ quantifies the deviation
from thermal equilibrium by data for the radial distribution function of 3d
Kob-Andersen and 2d Yukawa active-matter models with active Ornstein-Uhlenbeck
and active Brownian Particle dynamics. Moreover, we show that $\Ts/\Tc$,
structure, and dynamics of the homogeneous phase are all approximately
invariant along the motility-induced phase separation (MIPS) boundary in the
phase diagram of the 2d Yukawa model. The measure $\Ts/\Tc$ is not limited to
active matter; it can be used for quantifying how far any system involving a
potential-energy function, e.g., a driven Hamiltonian system, is from thermal
equilibrium.
