  We explore the possible Proxima Centauri b's interiors assuming the planet
belongs to the class of dense solid planets (rocky with possible addition of
water) and derive the corresponding radii. To do so, we use an internal
structure model that computes the radius of the planet along with the locations
of the different layers of materials, assuming that its mass and bulk
composition are known. Lacking detailed elementary abundances of the host star
to constrain the planet's composition, we base our model on solar system
values. We restrained the simulations to the case of solid planets without
massive atmospheres. With these assumptions, the possible radius of Proxima
Centauri b spans the 0.94--1.40 $R_\oplus$ range. The minimum value is obtained
considering a 1.10 $M_\oplus$ Mercury-like planet with a 65% core mass
fraction, whereas the highest radius is reached for 1.46 $M_\oplus$ with 50%
water in mass, constituting an ocean planet. Although this range of radii still
allows very different planet compositions, it helps characterizing many aspects
of Proxima Centauri b, such as the formation conditions of the system or the
current amount of water on the planet. This work can also help ruling out
future measurements of the planet's radius that would be physically
incompatible with a solid planetary body.
