  There is a broad theoretical consensus on the idea that ordinary neutrinos
have a Majorana mass, but we have no clear prediction about its value, and
direct experimental measurements of this quantity are rather challenging. In
this work, we argue that the current cosmological measurements allow us to
obtain precise information on the effective Majorana mass, i.e. the
electronic-type mass of ordinary neutrinos. We show that the numerical results
that we obtain can be accurately reproduced, and hence tested, by a
straightforward analytical procedure. We then discuss the stability of the
assumptions at the basis of our analysis and the implications of our findings
for neutrinoless double beta decay.
