A method that can be used to measure the absolute efficiency of narrow-track magnetic heads such as video heads (gap area <103(μm)2) is described. The method is based on the detection of the gap flux by means of a subsidiary coil wound around the gap. Usually a considerable amount of leakage flux is detected together with the gap flux, which obviously would impair the accuracy of the results. Therefore, measures were taken by raising the current through the main coil progressively and thus determining the saturation value of the gap flux. In this way it was possible to distinguish between the gap flux and leakage flux components. With this method the efficiency can be measured with an accuracy of better than 10 percent at frequencies of up to 10 MHz. As a second result, the gap area can thus be determined magnetically as well. A comparison of the magnetic and optical gap area offers a check on the reliability of the efficiency measurement. The merits of this measuring method are discussed with the aid of results obtained for a typical ferrite video head.