  The average helicity of a given electromagnetic field measures the difference
between the number of left- and right-handed photons contained in the field. In
here, the average helicity is derived using the conformally-invariant
inner-product for Maxwell fields. Several equivalent integral expressions in
momentum space, in $(\mathbf{r},t)$ space, and in the time-harmonic
$(\mathbf{r},\omega)$ space are obtained, featuring Riemann-Silberstein-like
fields and potentials. The time-harmonic expressions can be directly evaluated
using the outputs of common numerical solvers of Maxwell equations. The results
are shown to be equivalent to the well-known volume integral for the average
helicity, featuring the electric and magnetic fields and potentials.
