  A functional renormalisation group study for the BEC-BCS crossover for
ultracold gases of fermionic atoms is presented. We discuss the fixed point
which is at the origin of universality for broad Feshbach resonances. All
macroscopic quantities depend only on one relevant parameter, the concentration
a k_F, besides their dependence on the temperature in units of the Fermi
energy. In particular, we compute the universal ratio between molecular and
atomic scattering length in vacuum. We also present an estimate to which level
of accuracy universality holds for gases of Li and K atoms.
