Scaling laws have always played an important role in astronomy. They can give a general qualitative overview of common behaviors of many astrophysical objects, helping to understand the occurring physical processes. In the context of exoplanets, we study the possible correlation between (i) the planetary radius and the equilibrium temperature, [Formula: see text], and (ii) the planetary radius and the parent-star metallicity, [Formula: see text]. We considered a sample of transiting planets, for which their mass radius and equilibrium temperature are accurately determined. While we do not see any notable evidence of a correlation between [Formula: see text] and [Fe/H], the existence of a relationship between [Formula: see text] and [Formula: see text] is almost clear. We sub-divided our sample in different groups, based on their mass, and performed a least-squares regression of [Formula: see text] on [Formula: see text] for each sub-sample of planets. We found that the [Formula: see text] relation results very tight for two groups of intermediate-massive gas planets (i.e. for [Formula: see text] in the range between 0.5–1.0[Formula: see text][Formula: see text] and 1.0–1.5[Formula: see text][Formula: see text]) and that the slope of the best-fitting line gradually increases from the group of very massive to those of less massive planets, up to reverse in the Neptunian–Super-Earth regime, which has a negative correlation.