The masses and radii of 81 observed cool giant planets with 1σ errorbars, along with Jupiter, Saturn, Uranus and Neptune. The log₁₀ of the incident flux is indicated by the color, to show that it does not affect the radius. The fit and 1σ dispersion from Equation (2) and the posterior mean parameters are shown in blue. The relation from the structure models of (Thorngren et al. 2016) is shown in red, where the dispersion is from the uncertainty in the mass–metallicity relation.