The procedure of an experimental estimation of pressure of a magnetic field of a flat spiral inductor in system with a mobile element from good conduction is developed for processes electromagnetic stamping by polyurethane (EMSP). The procedure is based on measurement of magnetic density along a radial direction of a spiral by means of the induction sensor and effectiveness factor calculation. The system of the dimensionless parameters influencing effectiveness factor is offered. Empirical dependence of effectiveness factor on the dimensionless parameters is received. This dependence can be used in practice of calculations of the technological devices and technologies of EMSP.