We present quasar bolometric corrections using the [ O III] λ5007 narrow emission line luminosity based on the detailed spectral energy distributions of 53 bright quasars at low to moderate redshift (0.0345 < z < 1.0002). We adopted two functional forms to calculate Liso, the bolometric luminosity determined under the assumption of isotropy: L_ iso=A L[ O III]_ for comparison with the literature and log(L_ iso_)=B+C log(L_[ O III]_), which better characterizes the data. We also explored whether 'Eigenvector 1 (EV1)', which describes the range of quasar spectral properties and quantifies their diversity, introduces scatter into the L_[ O III]–Liso_ relationship. We found that the [ O III] bolometric correction can be significantly improved by adding a term including the equivalent width ratio R_ Fe II_≡ EW_ Fe II_/ EW_ Hβ_, which is an EV1 indicator. Inclusion of R_ Fe II_ in predicting Liso is significant at nearly the 3σ level and reduces the scatter and systematic offset of the luminosity residuals. Typically, [ O III] bolometric corrections are adopted for Type 2 sources where the quasar continuum is not observed and in these cases, R_ Fe II_ cannot be measured. We searched for an alternative measure of EV1 that could be measured in the optical spectra of Type 2 sources but were unable to identify one. Thus, the main contribution of this work is to present an improved [ O III] bolometric correction based on measured bolometric luminosities and highlight the EV1 dependence of the correction in Type 1 sources.