The non-isothermal crystallization of 11 different homopolymers and one copolymer is measured by fast differential scanning calorimetry (FDSC) with various cooling rates. A new method to evaluate the kinetics of polymer crystallization based on the Gibbs free energy difference between liquid and crystal is proposed. As a result a surface parameter, kappa, is introduced characterizing the surface free energy of the crystals in respect to the molecular packing density. Regarding this surface parameter the homopolymers can be grouped in three groups. Polyamides and polyesters behave differently compared to the other polymers investigated here. Inside a group of polymers the ratio between surface tension and crystalline package density is widely invariant regarding crystal perfectness and chemical structure.