  The flux ratio of Fe XXVI--Ly$\alpha$ to Fe XXV--He$\alpha$ lines ($I_{\rm
7.0}/I_{\rm 6.7}$) is a sensitive indicator of the maximum temperature ($T_{\rm
max}$), and therefore the mass of white dwarf stars ($M_{\rm WD}$) in
cataclysmic variables (CVs). To examine and calibrate the theoretical $I_{\rm
7.0}/I_{\rm 6.7}$--$T_{\rm max}$--$M_{\rm WD}$ relations, reliable measurements
of $T_{\rm max}$ and $I_{\rm 7.0}/I_{\rm 6.7}$ are necessary. In this work, we
conduct a thorough investigation on 3--50 keV X-ray spectra of 25 solar
neighborhood magnetic and non-magnetic CVs based on archival \textit{NuSTAR}
and \textit{Suzaku} observations. The measured $T_{\rm max}$ are compared to
the $I_{\rm 7.0}/I_{\rm 6.7}$ and $M_{\rm WD}$. The results show the sampled
CVs closely follow the theoretical $I_{\rm 7.0}/I_{\rm 6.7}$--$T_{\rm max}$
relation. Moreover, all the $M_{\rm WD}$ estimated from $I_{\rm 7.0}/I_{\rm
6.7}$ are consistent with the dynamically measured ones. We conclude that
$I_{\rm 7.0}/I_{\rm 6.7}$ can be used as a good diagnostic for $T_{\rm max}$
and $M_{\rm WD}$ in both magnetic and non-magnetic CVs.
