In C3, the cavity volume calculation is performed without requiring user-defined parameters, as the default settings yield satisfactory results across a wide range of cages. The algorithm starts by generating a box around the cage structure with dimensions to fit all cage atoms followed by the generation of a 3D grid. By default, the grid spacing is set to 1 Å, but users can modify it. For example, for cavity volumes exceeding 5000 Å 3 a grid size of 2 Å will be equally accurate and reduce computation time. The calculation of the cavity volume involves iterating over grid points and classifying them as either part of the cavity or outside of it. This selection involves two steps: