  We use recent lattice QCD outputs to work out the expansion law of the
Universe during the cosmological quark--hadron transition. To do so, a suitable
technique to exploit both pressure and energy density data, with the related
error bars, is introduced. We also implement suitable techniques to relate the
T range where lattice outputs are available with lower and higher T's, for
which we test suitable expressions. We finally compare the cosmological
behavior found using lattice data with the one obtainable in the case the
transition were first order, although not so far from the crossover transition
we studied. Differences are small to be tested with cosmological data, but the
coming of the era of precision cosmology might open a channel to inspect the
QCD transition through them.
