A closed-form solution for power balance equation of electric arc furnace (EAF) is proposed in this paper based on field measurements of the instantaneous furnace voltage and current. The method is developed based on an analytical solution of power balance equation in general case. The closed-form solution is dependent on the EAF parameters, which should be found by parameter identification procedure carrying out by minimization of an appropriate objective function. The minimization is performed by means of a calculus-based optimization method, namely, interior-point method. The validity of the proposed method is verified by comparing its results with those of the field measurements. The results show quite satisfactory correlation between the proposed method and the actual EAF operation.