  I use volume- and mass-limited subsamples and recently published data from
the Spitzer Survey of Stellar Structure in Galaxies (S4G) to investigate how
the size of bars depends on galaxy properties. The known correlation between
bar semi-major-axis $a$ and galaxy stellar mass (or luminosity) is actually
*bimodal*: for $\log M_{\star} < 10.1$, bar size is almost independent of
stellar mass ($a \propto M_{\star}^{0.1}$), while it is a strong function for
higher masses ($a \propto M_{\star}^{0.6}$). Bar size is a slightly stronger
function of galaxy half-light radius $r_{e}$ and (especially) exponential disc
scale length $h$ ($a \propto h^{0.8}$). Correlations between stellar mass and
galaxy size can explain the bar-size--$M_{\star}$ correlation -- but only for
galaxies with $\log M_{\star} < 10.1$; at higher masses, there is an extra
dependence of bar size on $M_{\star}$ itself. Despite theoretical arguments
that the presence of gas can affect bar growth, there is no evidence for any
residual dependence of bar size on (present-day) gas mass fraction. The
traditional dependence of bar size on Hubble type (longer bars in early-type
discs) can be explained as a side-effect of stellar-mass--Hubble-type
correlations. Finally, I show that galaxy size ($r_{e}$ or $h$) can be modeled
as a function of stellar mass and both bar presence and bar size: barred
galaxies tend to be more extended than unbarred galaxies of the same mass, with
larger bars correlated with larger sizes.
