Within the framework of Ginzburg-Landau (GL) theory we study the supercooling fields of pure tin films. We have systematically measured the supercooling field as functions of inverse thickness and temperature in both perpendicular and parallel orientations for films obtained by electrolytic deposition. By analyzing the solution of the linearized GL equation, we show that the GL parameter K of bulk material can be reliably obtained from the reduced supercooling field. The extrapolation to infinite thickness and to temperature close to the critical temperature of supercooling field allows to obtain the GL parameter of pure tin, the coherence length xi(0), the penetration depth lambda(0), the London penetration depth lambda(L)(0) and the zero-thermodynamic perpendicular critical field H-c(0). Our results are consistent with those obtained from supercooling fields of bulk spheres. They provide an explanation for discrepancy previously observed between values of the GL parameter in bulk samples and those deduced from superheating and supercooling fields on superconducting granules. Our results are compared with previous experimental work.