  abridged: We use a complete sample of about 140,000 galaxies from the Sloan
Digital Sky Survey (SDSS) to study the size distribution of galaxies and its
dependence on their luminosity, stellar mass, and morphological type. The large
SDSS database provides statistics of unprecedented accuracy. For each type of
galaxy, the size distribution at given luminosity (or stellar mass) is well
described by a log-normal function, characterized by its median $\bar{R}$ and
dispersion $\sigma_{\ln R}$. For late-type galaxies, there is a characteristic
luminosity at $M_{r,0}\sim -20.5$ (assuming $h=0.7$) corresponding to a stellar
mass $M_0\sim 10^{10.6}\Msun$. Galaxies more massive than $M_0$ have
$\bar{R}\propto M^{0.4}$ and $\sigma_{\ln R}\sim 0.3$, while less massive
galaxies have $\bar{R}\propto M^{0.15}$ and $\sigma_{\ln R}\sim 0.5$. For
early-type galaxies, the $\bar{R}$ - $M$ relation is significantly steeper,
$\bar{R}\propto M^{0.55}$, but the $\sigma_{\ln R}$ - $M$ relation is similar
to that of late-type galaxies. Faint red galaxies have sizes quite independent
of their luminosities.
