The surface area calculation implemented in RASPA2 follows a very standard "rolling ball" algorithm based on hard spheres with sizes determined by the sigma value of the Lennard-Jones potential. First, a probe-molecule samples the spherical surface of the atoms of the framework. A portion of the sphere is excluded, because the probe overlaps with another atom. Each framework atom has an area of adsorbable surface, and the sum of all the areas gives the total adsorbable surface area. The values given by these simulations are then compared to the values given by our algorithm to check the consistency of our implementation.