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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 data base 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  and dispersion σ_{ln R}. For late-type galaxies, there is a characteristic luminosity at M_r,0∼−20.5 (assuming h= 0.7) corresponding to a stellar mass M₀∼ 10^10.6 M_⊙. Galaxies more massive than M₀ have  and σ_{ln R}∼ 0.3, while less massive galaxies have  and σ_{ln R}∼ 0.5. For early-type galaxies, the  relation is significantly steeper, , but the σ_{ln R}–M relation is similar to that of bright late-type galaxies. Faint red galaxies have sizes quite independent of their luminosities …