  The planetary mass-radius diagram is an observational result of central
importance to understand planet formation. We present an updated version of our
planet formation model based on the core accretion paradigm which allows to
calculate planetary radii and luminosities during the entire formation and
evolution of the planets. We first study with it the formation of Jupiter, and
compare with previous works. Then we conduct planetary population synthesis
calculations to obtain a synthetic mass-radius diagram which we compare with
the observed one. Except for bloated Hot Jupiters which can be explained only
with additional mechanisms related to their proximity to the star, we find a
good agreement of the general shape of the observed and the synthetic
mass-radius diagram. This shape can be understood with basic concepts of the
core accretion model.
