  In this note, we derive a stability and weak-strong uniqueness principle for
volume-preserving mean curvature flow. The proof is based on a new notion of
volume-preserving gradient flow calibrations, which is a natural extension of
the concept in the case without volume preservation recently introduced by
Fischer et al. [arXiv:2003.05478]. The first main result shows that any strong
solution with certain regularity is calibrated. The second main result consists
of a stability estimate in terms of a relative entropy, which is valid in the
class of distributional solutions to volume-preserving mean curvature flow.
