  The Curie-Weiss law is widely used to estimate the strength of frustration in
frustrated magnets. However, the Curie-Weiss law was originally derived as an
estimate of magnetic correlations close to a mean-field phase transition, which
-- by definition -- is absent in spin liquids. Instead, the susceptibility of
spin liquids is known to undergo a Curie-law crossover between two magnetically
disordered regimes. Here, we study the generic aspect of the Curie-law
crossover by comparing a variety of frustrated spin models in two and three
dimensions, using both classical Monte Carlo simulations and analytical Husimi
tree calculations. Husimi tree calculations fit remarkably well the simulations
for all temperatures and almost all lattices. We also propose a Husimi Ansatz
for the reduced susceptibility $\chi T$, to be used in complement to the
traditional Curie-Weiss fit in order to estimate the Curie-Weiss temperature
$\theta_{\rm cw}$. Applications to materials are discussed.
