  The Poisson-Boltzmann (PB) equation provides a mean-field theory of
electrolyte solutions at interfaces and in confinement, with numerous
applications ranging from colloid science to nanofluidics. This formulary
gathers important formulas for the PB description of a Z:Z electrolyte solution
inside slit and cylindrical channels. Different approximated solutions (thin
electrical double layers, no co-ion, Debye-H\"uckel, and homogeneous/parabolic
potential limits) and their range of validity are discussed, together with the
full solution for the slit channel. In addition, different boundary conditions
are presented, the limits of the PB framework are briefly discussed, and Python
scripts to solve the PB equation numerically are provided.
