A scaling theory for spinodal decomposition in the inertial hydrodynamic re
gime is presented. The scaling involves three relevant length scales, the d
omain size, the Taylor microscale, and the Kolmogorov dissipation scale. Th
is allows for the presence of an inertial "energy cascade," familiar from t
heories of turbulence, and improves on earlier scaling treatments based on
a single length: these, it is shown, cannot be reconciled with energy conse
rvation. This theory reconciles the t(2/3) scaling of the domain size, pred
icted by simple scaling, with the physical expectation of a saturating Reyn
olds number at late times.