Last-orbit frequency of a compact binary
= Last-orbit frequency of a compact binary
As a heuristic approximation, inserting $r=6GM/c^2$ into the <circular orbit> form of <Kepler's third law>, with $M$ here denoting the total <mass>, gives
$$
T=12\pi\sqrt6\,\frac{GM}{c^3}.
$$
The dominant quadrupole gravitational-wave frequency is twice the orbital frequency, $f_{\rm GW}=2/T$.