  By combining molecular dynamics simulations and topological analyses with
scaling arguments, we obtain analytic expressions that quantitatively predict
the entanglement length $N_e$, the plateau modulus $G$, and the tube diameter
$a$ in melts that span the entire range of chain stiffnesses for which systems
remain isotropic. Our expressions resolve conflicts between previous scaling
predictions for the loosely entangled [Lin-Noolandi: $G\ell_K^3/k_\textrm{B}T
\sim (\ell_K/p)^3$], semiflexible [Edwards/de Gennes: $G\ell_K^3/k_\textrm{B}T
\sim (\ell_K/p)^2$], and tightly-entangled [Morse: $G\ell_K^3/k_\textrm{B}T
\sim (\ell_K/p)^{1+\epsilon}$] regimes, where $\ell_K$ and $p$ are respectively
the Kuhn and packing lengths. We also find that maximal entanglement (minimal
$N_e$) coincides with the onset of local nematic order.
