The paper investigates the size distribution of galaxies in the Sloan Digital Sky Survey (SDSS) and its dependence on luminosity, stellar mass, and morphological type. The study uses a complete sample of about 140,000 galaxies, providing unprecedented statistical accuracy. For each galaxy type, the size distribution at a given luminosity or stellar mass is well described by a log-normal function, characterized by a median radius \(\bar{R}\) and dispersion \(\sigma_{\ln R}\). Late-type galaxies show a characteristic luminosity \(M_L \sim -20.5\) corresponding to a stellar mass \(M_0 \sim 10^{10.6} \, \text{M}_\odot\), with \(\bar{R} \propto M^{0.4}\) and \(\sigma_{\ln R} \sim 0.3\) for massive galaxies, and \(\bar{R} \propto M^{0.15}\) and \(\sigma_{\ln R} \sim 0.5\) for less massive galaxies. Early-type galaxies exhibit a steeper \(\bar{R} - M\) relation, \(\bar{R} \propto M^{0.55}\), but similar \(\sigma_{\ln R} - M\) relations as bright late-type galaxies. Faint red galaxies have sizes independent of luminosity. The observed relations are interpreted using theoretical models, suggesting that the fraction of baryons forming stars aligns with the standard feedback model, and that bulge formation maintains a marginally stable disk. The results have implications for the formation and evolution of galaxies, particularly for elliptical galaxies.The paper investigates the size distribution of galaxies in the Sloan Digital Sky Survey (SDSS) and its dependence on luminosity, stellar mass, and morphological type. The study uses a complete sample of about 140,000 galaxies, providing unprecedented statistical accuracy. For each galaxy type, the size distribution at a given luminosity or stellar mass is well described by a log-normal function, characterized by a median radius \(\bar{R}\) and dispersion \(\sigma_{\ln R}\). Late-type galaxies show a characteristic luminosity \(M_L \sim -20.5\) corresponding to a stellar mass \(M_0 \sim 10^{10.6} \, \text{M}_\odot\), with \(\bar{R} \propto M^{0.4}\) and \(\sigma_{\ln R} \sim 0.3\) for massive galaxies, and \(\bar{R} \propto M^{0.15}\) and \(\sigma_{\ln R} \sim 0.5\) for less massive galaxies. Early-type galaxies exhibit a steeper \(\bar{R} - M\) relation, \(\bar{R} \propto M^{0.55}\), but similar \(\sigma_{\ln R} - M\) relations as bright late-type galaxies. Faint red galaxies have sizes independent of luminosity. The observed relations are interpreted using theoretical models, suggesting that the fraction of baryons forming stars aligns with the standard feedback model, and that bulge formation maintains a marginally stable disk. The results have implications for the formation and evolution of galaxies, particularly for elliptical galaxies.