Calculating solubility parameters requires selecting features of a molecule that contribute to its behavior, fixing a value to it, and combing all the relevant components to give a total value. The basic formula used to compute the HSP is:
HSP2 = 4δP2 + δD2 + δH2
where δP is the contribution from dipolar intermolecular forces, δD is the contribution from dispersion forces, and δH comes from hydrogen bonds between molecules. Why the squares in the formula? It’s like the Pythagorean Theorem, except in three dimensions.