  The unified form of longitudinal optical conductivities (LOCs) in the tilted
Weyl fermions for arbitrary spatial dimensionality are analytically calculated
and expressed in terms of the joint density of state. The results are valid for
both undoped and doped cases, both parallel and perpendicular components, and
all the tilted phases. In addition, they reproduce analytical results of
previous works for one-dimensional, two-dimensional, and three-dimensional
tilted Weyl systems. The robust fixed point
$\Gamma_{\chi}^{(\mathrm{IB})}(\omega=2\mu,d\ge 2;\mu,0<t\le 2)=1/2$ is
universal for tilted Dirac bands in arbitrary spatial dimensionality. Our work
provides not only a once-for-all method prior to the one-by-one calculation of
the LOCs but also offer deep insights into the impacts of dimensionality in the
tilted Weyl fermions.
