I use volume- and mass-limited subsamples and recently published data from the Spitzer Survey of Stellar Structure in Galaxies ( S ^ { 4 } G ) 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 } / M _ { \sun } ) \la 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 } / M _ { \sun } ) \la 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 .