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This article explains the generation and use of a single curve which can be utilized in predicting, with reasonably high accuracy, the apparent inductance of all toroidal inductors at any operating frequency. Until the curve being discussed in this paper was developed, a separate curve was required for each different inductor. These individual curves were laboriously constructed by successive computations by each user. Utilizing the proposed procedure considerably reduces the number and complexity of the calculations, yet produces the desired results. Included in the text is a detailed explanation of the procedure used in developing this single curve and several examples depicting its use. To prove the validity of this method of predicting apparent inductance, a number of samples from various manufacturers of toroidal inductors were tested over a wide range of operating frequencies with extremely good results. Utilizing the curve not only aids in the proper design selection of toroidal inductors, but may result in the use of more available standard stocked items. Stocked items will prove more economical than specially designed units, will make use of already established reliability information, and will expedite procurement of parts.