  We examine the dependence of polycyclic aromatic hydrocarbon (PAH) band
intensity ratios as a function of the average number of carbon atoms and assess
their effectiveness as tracers for PAH size, utilising the data, models, and
tools provided by the NASA Ames PAH Infrared Spectroscopic Database. To achieve
this, we used spectra from mixtures of PAHs of different ionisation fractions,
following a size distribution. Our work, congruent with earlier findings, shows
that band ratios that include the 3.3 ${\mu}$m PAH band provide the best PAH
size tracers for small-to-intermediate sized PAHs. In addition, we find that
band ratios that include the sum of the 15-20 ${\mu}$m PAH features
(I$_{\Sigma_{15-20}}$) and the 6.2 or 7.7 ${\mu}$m bands also serve as good
tracers for PAH size in the case of small-to-intermediate sized PAHs, for
objects under a similar PAH size distribution as with the presented models. For
different PAH size distributions, the application of a scaling factor to the
I$_{6.2}$/I$_{\Sigma_{15-20}}$ ratio can provide estimates for the size of the
small-to-intermediate PAH population within sources. Employment of the
I$_{6.2}$/I$_{\Sigma_{15-20}}$ and I$_{7.7}$/I$_{\Sigma_{15-20}}$ ratios can be
of particular interest for JWST observations limited only to $\sim$ 5-28
${\mu}$m MIRI(-MRS) coverage.
