  We present a calculation of the finite volume corrections to meson masses and
decay constants in three flavour Partially Quenched Chiral Perturbation Theory
(PQChPT) through two-loop order in the chiral expansion for the flavour-charged
(or off-diagonal) pseudoscalar mesons. The analytical results are obtained for
three sea quark flavours with one, two or three different masses. We reproduce
the known infinite volume results and the finite volume results in the
unquenched case. The calculation has been performed using the supersymmetric
formulation of PQChPT as well as with a quark-flow technique.
  Partial analytical results can be found in the appendices. Some examples of
cases relevant to lattice QCD are studied numerically. Numerical programs for
all results are available as part of the CHIRON package.
