  Historically, emission lines have been considered a valuable tool for
estimating the bolometric thermal luminosity of the accretion flow in AGN,
$L_{bol}$. We study the reliability of this method by comparing line strengths
to the optical/UV continuum luminosity of SDSS DR7 radio quiet quasars with
$0.4<z<0.8$. We find formulae for $L_{bol}$ as a function of single line
strengths for the broad components of H$\beta$ and Mg II, as well as the narrow
lines of [O III] and [O II]. We determine the standard errors of the formulae
that are fitted to the data. Our new estimators are shown to be more accurate
than archival line strength estimations in the literature. It is demonstrated
that the broad lines are superior estimators of the continuum luminosity (and
$L_{bol}$) with $H\beta$ being the most reliable. The fidelity of the each of
the estimators is determined in the context of the SDSS DR7 radio loud quasars
as an illustrative application of our results. In general, individual
researchers can use our results as a tool to help decide if a particular line
strength provides an adequate estimate of $L_{bol}$ for their purposes.
Finally, it is shown that considering all four line strength, simultaneously,
can yield information on both $L_{bol}$ and the radio jet power.
