We can calculate the radius of an exoplanet thanks to the transit method because relates the radius to the luminosity and the radius of the star with respect to the sun
Here you have a scheme:
The formula with which we calculate the radius is the following: R=√(1-Brightness) · Radius of the star with respect to the sun-> We have to multiplicate the result x100.
Example of 16 Cyg B b with my own data
R=√(1-Brightness) · Radius of the star with respect to the sun -> R=√(1-0,9998) · 1,159= 0,01639-> 0,01639·100=1,6
We can conclude that the exoplanet 16 Cyg B b is about 1.6 times the radius of the earth.