  We present the size-stellar mass relations of nearby (z=0.01-0.02) Sloan
Digital Sky Survey galaxies, for samples selected by color, morphology, Sersic
index n, and specific star formation rate. Several commonly employed size
measurement techniques are used, including single Sersic fits, two-component
Sersic models, and a non-parametric method. Through simple simulations, we show
that the non-parametric and two-component Sersic methods provide the most
robust effective radius measurements, while those based on single Sersic
profiles are often overestimates, especially for massive red/early-type
galaxies. Using our robust sizes, we show for all sub-samples that the
mass-size relations are shallow at low stellar masses and steepen above ~ 3-4 x
10^{10}\msun. The mass-size relations for galaxies classified as late-type,
low-n, and star-forming are consistent with each other, while blue galaxies
follow a somewhat steeper relation. The mass-size relations of early-type,
high-n, red, and quiescent galaxies all agree with each other but are somewhat
steeper at the high-mass end than previous results. To test potential
systematics at high redshift, we artificially redshifted our sample (including
surface brightness dimming and degraded resolution) to z=1 and re-fit the
galaxies using single Serisc profiles. The sizes of these galaxies before and
after redshifting are consistent and we conclude that systematic effects in
sizes and the size-mass relation at z ~ 1 are negligible. Interestingly, since
the poorer physical resolution at high redshift washes out bright galaxy
substructures, single-Sersic fitting appears to provide more reliable and
unbiased effective radius measurements at high z than for nearby, well-resolved
galaxies.
