  To aid in the physical interpretation of planetary radii constrained through
observations of transiting planets, or eventually direct detections, we compute
model radii of pure hydrogen-helium, water, rock, and iron planets, along with
various mixtures. Masses ranging from 0.01 Earth masses to 10 Jupiter masses at
orbital distances of 0.02 to 10 AU are considered. For hydrogen-helium rich
planets, our models are the first to couple planetary evolution to stellar
irradiation over a wide range of orbital separations (0.02 to 10 AU) through a
non-gray radiative-convective equilibrium atmosphere model. Stellar irradiation
retards the contraction of giant planets, but its effect is not a simple
function of the irradiation level: a planet at 1 AU contracts as slowly as a
planet at 0.1 AU. For hydrogen-helium planets, we consider cores up to 90% of
the total planet mass, comparable to those of Uranus and Neptune. If "hot
Neptunes" have maintained their original masses and are not remnants of more
massive planets, radii of 0.30-0.45 times Jupiter's radius are expected. Water
planets are ~40-50% larger than rocky planets, independent of mass. Finally, we
provide tables of planetary radii at various ages and compositions, and for
ice-rock-iron planets we fit our results to analytic functions, which will
allow for quick composition estimates, given masses and radii, or mass
estimates, given only planetary radii. These results will assist in the
interpretation of observations for both the current transiting planet surveys
as well as upcoming space missions, including CoRoT and Kepler.
