  In the setting of a metric space equipped with a doubling measure that
supports a Poincar\'e inequality, we show that a set $E$ is of finite perimeter
if and only if $\mathcal H(\partial^1 I_E)<\infty$, that is, if and only if the
codimension one Hausdorff measure of the \emph{$1$-fine boundary} of the set's
measure theoretic interior $I_E$ is finite.
