We present quasar bolometric corrections using the $[{\rm O}\,\small {III}]\,\lambda 5007$ 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 L_iso, the bolometric luminosity determined under the assumption of isotropy: ${\rm L_{{\rm iso}}}=A\,{L_{[{\rm O}\,\small {III}]}}$ for comparison with the literature and ${\rm log(L_{{\rm iso}})}=B+C\,{\rm log}(L_{[{\rm O}\,\small {III}]})$, 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 $L_{[{\rm O}\,\small {III}]}$–L_iso relationship. We found that the ${[{\rm O}\,\small {III}]}$ bolometric correction can be significantly improved by adding a term including the equivalent width ratio $R_{{\rm Fe}\,\small {II}}$$\equiv\, {\rm EW}_{{\rm Fe \small {II}}}/{\rm EW}_{{\rm H}\beta }$, which is an EV1 indicator. Inclusion of $R_{{\rm Fe}\,\small {II}}$ in predicting L_iso is significant at nearly the 3σ level and reduces the scatter and systematic offset of the luminosity residuals. Typically, ${[{\rm O}\,\small {III}]}$ bolometric corrections are adopted for Type 2 sources where the quasar continuum is not observed and in these cases, $R_{{\rm Fe}\,\small {II}}$ 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 ${[{\rm O}\,\small {III}]}$ bolometric correction based on measured bolometric luminosities and highlight the EV1 dependence of the correction in Type 1 sources.